item.h

#ifndef ITEM_INCLUDED
#define ITEM_INCLUDED

/* Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights
   reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */


#include "sql_priv.h"                /* STRING_BUFFER_USUAL_SIZE */
#include "unireg.h"
#include "sql_const.h"                 /* RAND_TABLE_BIT, MAX_FIELD_NAME */
#include "unireg.h"                    // REQUIRED: for other includes
#include "thr_malloc.h"                         /* sql_calloc */
#include "sql_array.h"
#include "sql_string.h"
#include "mysqld.h"
#include "table.h"
#include "my_decimal.h"                         /* my_decimal */
#include "sql_error.h"                          /* Sql_condition */
#include "mysql_version.h"                      /* FRM_VER */


class Protocol;
struct TABLE_LIST;
void item_init(void);			/* Init item functions */
class Item_field;
class user_var_entry;

typedef Bounds_checked_array<Item*> Ref_ptr_array;

static inline uint32
char_to_byte_length_safe(uint32 char_length_arg, uint32 mbmaxlen_arg)
{
   ulonglong tmp= ((ulonglong) char_length_arg) * mbmaxlen_arg;
   return (tmp > UINT_MAX32) ? (uint32) UINT_MAX32 : (uint32) tmp;
}

/**
 Tests if field type is temporal, i.e. represents
 DATE, TIME, DATETIME or TIMESTAMP types in SQL.

 @param type    Field type, as returned by field->type().
 @retval true   If field type is temporal
 @retval false  If field type is not temporal
 */
inline bool is_temporal_type(enum_field_types type) {
  switch (type) {
    case MYSQL_TYPE_TIME:
    case MYSQL_TYPE_DATETIME:
    case MYSQL_TYPE_TIMESTAMP:
    case MYSQL_TYPE_DATE:
    case MYSQL_TYPE_NEWDATE:
      return true;
    default:
      return false;
  }
}



/**
  Tests if field real type is temporal, i.e. represents
  all existing implementations of
  DATE, TIME, DATETIME or TIMESTAMP types in SQL.

  @param type    Field real type, as returned by field->real_type()
  @retval true   If field real type is temporal
  @retval false  If field real type is not temporal
*/
inline bool is_temporal_real_type(enum_field_types type)
{
  switch (type)
  {
    case MYSQL_TYPE_TIME2:
    case MYSQL_TYPE_TIMESTAMP2:
    case MYSQL_TYPE_DATETIME2:
      return true;
    default:
      return is_temporal_type(type);
  }
}


/**
  Tests if field real type can have "DEFAULT CURRENT_TIMESTAMP",
  i.e. represents TIMESTAMP types in SQL.

  @param type    Field type, as returned by field->real_type().
  @retval true   If field real type can have "DEFAULT CURRENT_TIMESTAMP".
  @retval false  If field real type can not have "DEFAULT CURRENT_TIMESTAMP".
*/
inline bool real_type_with_now_as_default(enum_field_types type)
{
  return type == MYSQL_TYPE_TIMESTAMP || type == MYSQL_TYPE_TIMESTAMP2 ||
         type == MYSQL_TYPE_DATETIME || type == MYSQL_TYPE_DATETIME2;
}


/**
  Tests if field real type can have "ON UPDATE CURRENT_TIMESTAMP",
  i.e. represents TIMESTAMP types in SQL.

  @param type    Field type, as returned by field->real_type().
  @retval true   If field real type can have "ON UPDATE CURRENT_TIMESTAMP".
  @retval false  If field real type can not have "ON UPDATE CURRENT_TIMESTAMP".
*/
inline bool real_type_with_now_on_update(enum_field_types type)
{
  return type == MYSQL_TYPE_TIMESTAMP || type == MYSQL_TYPE_TIMESTAMP2 ||
         type == MYSQL_TYPE_DATETIME || type == MYSQL_TYPE_DATETIME2;
}



/**
   Recognizer for concrete data type (called real_type for some reason),
   returning true if it is one of the TIMESTAMP types.
*/
inline bool is_timestamp_type(enum_field_types type)
{
  return type == MYSQL_TYPE_TIMESTAMP || type == MYSQL_TYPE_TIMESTAMP2;
}


inline uint get_enum_pack_length(int elements)
{
  return elements < 256 ? 1 : 2;
}


inline uint get_set_pack_length(int elements)
{
  uint len= (elements + 7) / 8;
  return len > 4 ? 8 : len;
}

enum utype  { NONE,DATE,SHIELD,NOEMPTY,CASEUP,PNR,BGNR,PGNR,YES,NO,REL,
  CHECK,EMPTY,UNKNOWN_FIELD,CASEDN,NEXT_NUMBER,INTERVAL_FIELD,
  BIT_FIELD, TIMESTAMP_OLD_FIELD, CAPITALIZE, BLOB_FIELD,
  TIMESTAMP_DN_FIELD, TIMESTAMP_UN_FIELD, TIMESTAMP_DNUN_FIELD};

enum geometry_type
{
  GEOM_GEOMETRY = 0, GEOM_POINT = 1, GEOM_LINESTRING = 2, GEOM_POLYGON = 3,
  GEOM_MULTIPOINT = 4, GEOM_MULTILINESTRING = 5, GEOM_MULTIPOLYGON = 6,
  GEOM_GEOMETRYCOLLECTION = 7
};

/*
  Create field class for CREATE TABLE
*/

class Create_field :public Sql_alloc
{
public:
  const char *field_name;
  const char *change;			// If done with alter table
  const char *after;			// Put column after this one
  LEX_STRING comment;			// Comment for field

  /**
     The declared default value, if any, otherwise NULL. Note that this member
     is NULL if the default is a function. If the column definition has a
     function declared as the default, the information is found in
     Create_field::unireg_check.

     @see Create_field::unireg_check
  */
  Item *def;
  enum	enum_field_types sql_type;
  /*
    At various stages in execution this can be length of field in bytes or
    max number of characters.
  */
  ulong length;
  /*
    The value of `length' as set by parser: is the number of characters
    for most of the types, or of bytes for BLOBs or numeric types.
  */
  uint32 char_length;
  uint  decimals, flags, pack_length, key_length;
  utype unireg_check;
  TYPELIB *interval;			// Which interval to use
  TYPELIB *save_interval;               // Temporary copy for the above
  // Used only for UCS2 intervals
  List<String> interval_list;
  const CHARSET_INFO *charset;
  geometry_type geom_type;

  uint8 row,col,sc_length,interval_id;	// For rea_create_table
  uint	offset,pack_flag;
  Create_field() :after(NULL) {}
  /* Used to make a clone of this object for ALTER/CREATE TABLE */
  Create_field *clone(MEM_ROOT *mem_root) const
  { return new (mem_root) Create_field(*this); }
  void create_length_to_internal_length(void);


  bool init(THD *thd, const char *field_name, enum_field_types type,
            const char *length, const char *decimals, uint type_modifier,
            Item *default_value, Item *on_update_value, LEX_STRING *comment,
            const char *change, List<String> *interval_list,
            const CHARSET_INFO *cs, uint uint_geom_type);
};

/*
   "Declared Type Collation"
   A combination of collation and its derivation.

  Flags for collation aggregation modes:
  MY_COLL_ALLOW_SUPERSET_CONV  - allow conversion to a superset
  MY_COLL_ALLOW_COERCIBLE_CONV - allow conversion of a coercible value
                                 (i.e. constant).
  MY_COLL_ALLOW_CONV           - allow any kind of conversion
                                 (combination of the above two)
  MY_COLL_ALLOW_NUMERIC_CONV   - if all items were numbers, convert to
                                 @@character_set_connection
  MY_COLL_DISALLOW_NONE        - don't allow return DERIVATION_NONE
                                 (e.g. when aggregating for comparison)
  MY_COLL_CMP_CONV             - combination of MY_COLL_ALLOW_CONV
                                 and MY_COLL_DISALLOW_NONE
*/

#define MY_COLL_ALLOW_SUPERSET_CONV   1
#define MY_COLL_ALLOW_COERCIBLE_CONV  2
#define MY_COLL_DISALLOW_NONE         4
#define MY_COLL_ALLOW_NUMERIC_CONV    8

#define MY_COLL_ALLOW_CONV (MY_COLL_ALLOW_SUPERSET_CONV | MY_COLL_ALLOW_COERCIBLE_CONV)
#define MY_COLL_CMP_CONV   (MY_COLL_ALLOW_CONV | MY_COLL_DISALLOW_NONE)


#define my_charset_numeric my_charset_latin1
#define MY_REPERTOIRE_NUMERIC   MY_REPERTOIRE_ASCII



enum Derivation
{
  DERIVATION_IGNORABLE= 6,
  DERIVATION_NUMERIC= 5,
  DERIVATION_COERCIBLE= 4,
  DERIVATION_SYSCONST= 3,
  DERIVATION_IMPLICIT= 2,
  DERIVATION_NONE= 1,
  DERIVATION_EXPLICIT= 0
};


class DTCollation {
public:
  const CHARSET_INFO *collation;
  enum Derivation derivation;
  uint repertoire;

  void set_repertoire_from_charset(const CHARSET_INFO *cs)
  {
    repertoire= cs->state & MY_CS_PUREASCII ?
                MY_REPERTOIRE_ASCII : MY_REPERTOIRE_UNICODE30;
  }
  DTCollation()
  {
    collation= &my_charset_bin;
    derivation= DERIVATION_NONE;
    repertoire= MY_REPERTOIRE_UNICODE30;
  }
  DTCollation(const CHARSET_INFO *collation_arg, Derivation derivation_arg)
  {
    collation= collation_arg;
    derivation= derivation_arg;
    set_repertoire_from_charset(collation_arg);
  }
  void set(DTCollation &dt)
  {
    collation= dt.collation;
    derivation= dt.derivation;
    repertoire= dt.repertoire;
  }
  void set(const CHARSET_INFO *collation_arg, Derivation derivation_arg)
  {
    collation= collation_arg;
    derivation= derivation_arg;
    set_repertoire_from_charset(collation_arg);
  }
  void set(const CHARSET_INFO *collation_arg,
           Derivation derivation_arg,
           uint repertoire_arg)
  {
    collation= collation_arg;
    derivation= derivation_arg;
    repertoire= repertoire_arg;
  }
  void set_numeric()
  {
    collation= &my_charset_numeric;
    derivation= DERIVATION_NUMERIC;
    repertoire= MY_REPERTOIRE_NUMERIC;
  }
  void set(const CHARSET_INFO *collation_arg)
  {
    collation= collation_arg;
    set_repertoire_from_charset(collation_arg);
  }
  void set(Derivation derivation_arg)
  { derivation= derivation_arg; }
  void set_repertoire(uint repertoire_arg)
  { repertoire= repertoire_arg; }
  bool aggregate(DTCollation &dt, uint flags= 0);
  bool set(DTCollation &dt1, DTCollation &dt2, uint flags= 0)
  { set(dt1); return aggregate(dt2, flags); }
  const char *derivation_name() const
  {
    switch(derivation)
    {
      case DERIVATION_NUMERIC:   return "NUMERIC";
      case DERIVATION_IGNORABLE: return "IGNORABLE";
      case DERIVATION_COERCIBLE: return "COERCIBLE";
      case DERIVATION_IMPLICIT:  return "IMPLICIT";
      case DERIVATION_SYSCONST:  return "SYSCONST";
      case DERIVATION_EXPLICIT:  return "EXPLICIT";
      case DERIVATION_NONE:      return "NONE";
      default: return "UNKNOWN";
    }
  }
};

/*************************************************************************/

/**
  Storage for name strings.
  Enpowers Simple_cstring with allocation routines from the sql_strmake family.

  This class must stay as small as possible as we often 
  pass it into functions using call-by-value evaluation.

  Don't add new members or virual methods into this class!
*/
class Name_string: public Simple_cstring
{
private:
  void set_or_copy(const char *str, size_t length, bool is_null_terminated)
  {
    if (is_null_terminated)
      set(str, length);
    else
      copy(str, length);  
  }
public:
  Name_string(): Simple_cstring() {}
  /*
    Please do NOT add constructor Name_string(const char *str) !
    It will involve hidden strlen() call, which can affect
    performance negatively. Use Name_string(str, len) instead.
  */
  Name_string(const char *str, size_t length):
    Simple_cstring(str, length) {}
  Name_string(const LEX_STRING str): Simple_cstring(str) {}
  Name_string(const char *str, size_t length, bool is_null_terminated):
    Simple_cstring()
  {
    set_or_copy(str, length, is_null_terminated);
  }
  Name_string(const LEX_STRING str, bool is_null_terminated):
    Simple_cstring()
  {
    set_or_copy(str.str, str.length, is_null_terminated);
  }
  /**
    Allocate space using sql_strmake() or sql_strmake_with_convert().
  */
  void copy(const char *str, size_t length, const CHARSET_INFO *cs);
  /**
    Variants for copy(), for various argument combinations.
  */
  void copy(const char *str, size_t length)
  {
    copy(str, length, system_charset_info);
  }
  void copy(const char *str)
  {
    copy(str, (str ? strlen(str) : 0), system_charset_info);
  }
  void copy(const LEX_STRING lex)
  {
    copy(lex.str, lex.length);
  }
  void copy(const LEX_STRING *lex)
  {
    copy(lex->str, lex->length);
  }
  void copy(const Name_string str)
  {
    copy(str.ptr(), str.length());
  }
};


#define NAME_STRING(x)  Name_string(C_STRING_WITH_LEN(x))


extern const Name_string null_name_string;


/**
  Storage for Item names.
  Adds "autogenerated" flag and warning functionality to Name_string.
*/
class Item_name_string: public Name_string
{
private:
  bool m_is_autogenerated; /* indicates if name of this Item
                              was autogenerated or set by user */
public:
  Item_name_string(): Name_string(), m_is_autogenerated(true)
  { }
  Item_name_string(const Name_string name)
    :Name_string(name), m_is_autogenerated(true)
  { }
  /**
    Set m_is_autogenerated flag to the given value.
  */
  void set_autogenerated(bool is_autogenerated)
  {
    m_is_autogenerated= is_autogenerated;
  }
  /**
    Return the auto-generated flag.
  */
  bool is_autogenerated() const { return m_is_autogenerated; }
  using Name_string::copy;
  /**
    Copy name together with autogenerated flag.
    Produce a warning if name was cut.
  */
  void copy(const char *str_arg, size_t length_arg, const CHARSET_INFO *cs_arg,
           bool is_autogenerated_arg);
};


void dummy_error_processor(THD *thd, void *data);

void view_error_processor(THD *thd, void *data);

/*
  Instances of Name_resolution_context store the information necesary for
  name resolution of Items and other context analysis of a query made in
  fix_fields().

  This structure is a part of SELECT_LEX, a pointer to this structure is
  assigned when an item is created (which happens mostly during  parsing
  (sql_yacc.yy)), but the structure itself will be initialized after parsing
  is complete

  TODO: move subquery of INSERT ... SELECT and CREATE ... SELECT to
  separate SELECT_LEX which allow to remove tricks of changing this
  structure before and after INSERT/CREATE and its SELECT to make correct
  field name resolution.
*/
struct Name_resolution_context: Sql_alloc
{
  /*
    The name resolution context to search in when an Item cannot be
    resolved in this context (the context of an outer select)
  */
  Name_resolution_context *outer_context;

  /*
    List of tables used to resolve the items of this context.  Usually these
    are tables from the FROM clause of SELECT statement.  The exceptions are
    INSERT ... SELECT and CREATE ... SELECT statements, where SELECT
    subquery is not moved to a separate SELECT_LEX.  For these types of
    statements we have to change this member dynamically to ensure correct
    name resolution of different parts of the statement.
  */
  TABLE_LIST *table_list;
  /*
    In most cases the two table references below replace 'table_list' above
    for the purpose of name resolution. The first and last name resolution
    table references allow us to search only in a sub-tree of the nested
    join tree in a FROM clause. This is needed for NATURAL JOIN, JOIN ... USING
    and JOIN ... ON. 
  */
  TABLE_LIST *first_name_resolution_table;
  /*
    Last table to search in the list of leaf table references that begins
    with first_name_resolution_table.
  */
  TABLE_LIST *last_name_resolution_table;

  /*
    SELECT_LEX item belong to, in case of merged VIEW it can differ from
    SELECT_LEX where item was created, so we can't use table_list/field_list
    from there
  */
  st_select_lex *select_lex;

  /*
    Processor of errors caused during Item name resolving, now used only to
    hide underlying tables in errors about views (i.e. it substitute some
    errors for views)
  */
  void (*error_processor)(THD *, void *);
  void *error_processor_data;

  /**
    When TRUE, items are resolved in this context against
    SELECT_LEX::item_list, SELECT_lex::group_list and
    this->table_list. If FALSE, items are resolved only against
    this->table_list.

    @see st_select_lex::item_list, st_select_lex::group_list
  */
  bool resolve_in_select_list;

  Name_resolution_context()
    :outer_context(0), table_list(0), select_lex(0),
    error_processor_data(0)
    {}

  void init()
  {
    resolve_in_select_list= FALSE;
    error_processor= &dummy_error_processor;
    first_name_resolution_table= NULL;
    last_name_resolution_table= NULL;
  }

  void resolve_in_table_list_only(TABLE_LIST *tables)
  {
    table_list= first_name_resolution_table= tables;
    resolve_in_select_list= FALSE;
  }

  void process_error(THD *thd)
  {
    (*error_processor)(thd, error_processor_data);
  }
};


/*
  Store and restore the current state of a name resolution context.
*/

class Name_resolution_context_state
{
private:
  TABLE_LIST *save_table_list;
  TABLE_LIST *save_first_name_resolution_table;
  TABLE_LIST *save_next_name_resolution_table;
  bool        save_resolve_in_select_list;
  TABLE_LIST *save_next_local;

public:
  Name_resolution_context_state() {}          /* Remove gcc warning */

public:
  /* Save the state of a name resolution context. */
  void save_state(Name_resolution_context *context, TABLE_LIST *table_list)
  {
    save_table_list=                  context->table_list;
    save_first_name_resolution_table= context->first_name_resolution_table;
    save_resolve_in_select_list=      context->resolve_in_select_list;
    save_next_local=                  table_list->next_local;
    save_next_name_resolution_table=  table_list->next_name_resolution_table;
  }

  /* Restore a name resolution context from saved state. */
  void restore_state(Name_resolution_context *context, TABLE_LIST *table_list)
  {
    table_list->next_local=                save_next_local;
    table_list->next_name_resolution_table= save_next_name_resolution_table;
    context->table_list=                   save_table_list;
    context->first_name_resolution_table=  save_first_name_resolution_table;
    context->resolve_in_select_list=       save_resolve_in_select_list;
  }

  TABLE_LIST *get_first_name_resolution_table()
  {
    return save_first_name_resolution_table;
  }
};


/*
  This enum is used to report information about monotonicity of function
  represented by Item* tree.
  Monotonicity is defined only for Item* trees that represent table
  partitioning expressions (i.e. have no subselects/user vars/PS parameters
  etc etc). An Item* tree is assumed to have the same monotonicity properties
  as its correspoinding function F:

  [signed] longlong F(field1, field2, ...) {
    put values of field_i into table record buffer;
    return item->val_int(); 
  }

  NOTE
  At the moment function monotonicity is not well defined (and so may be
  incorrect) for Item trees with parameters/return types that are different
  from INT_RESULT, may be NULL, or are unsigned.
  It will be possible to address this issue once the related partitioning bugs
  (BUG#16002, BUG#15447, BUG#13436) are fixed.

  The NOT_NULL enums are used in TO_DAYS, since TO_DAYS('2001-00-00') returns
  NULL which puts those rows into the NULL partition, but
  '2000-12-31' < '2001-00-00' < '2001-01-01'. So special handling is needed
  for this (see Bug#20577).
*/

typedef enum monotonicity_info 
{
   NON_MONOTONIC,              /* none of the below holds */
   MONOTONIC_INCREASING,       /* F() is unary and (x < y) => (F(x) <= F(y)) */
   MONOTONIC_INCREASING_NOT_NULL,  /* But only for valid/real x and y */
   MONOTONIC_STRICT_INCREASING,/* F() is unary and (x < y) => (F(x) <  F(y)) */
   MONOTONIC_STRICT_INCREASING_NOT_NULL  /* But only for valid/real x and y */
} enum_monotonicity_info;

/*************************************************************************/

class sp_rcontext;


class Settable_routine_parameter
{
public:
  /*
    Set required privileges for accessing the parameter.

    SYNOPSIS
      set_required_privilege()
        rw        if 'rw' is true then we are going to read and set the
                  parameter, so SELECT and UPDATE privileges might be
                  required, otherwise we only reading it and SELECT
                  privilege might be required.
  */
  Settable_routine_parameter() {}
  virtual ~Settable_routine_parameter() {}
  virtual void set_required_privilege(bool rw) {};
};


typedef bool (Item::*Item_processor) (uchar *arg);
/*
  Analyzer function
    SYNOPSIS
      argp   in/out IN:  Analysis parameter
                    OUT: Parameter to be passed to the transformer

    RETURN 
      TRUE   Invoke the transformer
      FALSE  Don't do it

*/
typedef bool (Item::*Item_analyzer) (uchar **argp);
typedef Item* (Item::*Item_transformer) (uchar *arg);
typedef void (*Cond_traverser) (const Item *item, void *arg);


class Item
{
  Item(const Item &);			/* Prevent use of these */
  void operator=(Item &);
  /* Cache of the result of is_expensive(). */
  int8 is_expensive_cache;
  virtual bool is_expensive_processor(uchar *arg) { return 0; }

public:
  static void *operator new(size_t size) throw ()
  { return sql_alloc(size); }
  static void *operator new(size_t size, MEM_ROOT *mem_root) throw ()
  { return alloc_root(mem_root, size); }
  static void operator delete(void *ptr,size_t size) { TRASH(ptr, size); }
  static void operator delete(void *ptr, MEM_ROOT *mem_root) {}

  enum Type {FIELD_ITEM= 0, FUNC_ITEM, SUM_FUNC_ITEM, STRING_ITEM,
	     INT_ITEM, REAL_ITEM, NULL_ITEM, VARBIN_ITEM,
	     COPY_STR_ITEM, FIELD_AVG_ITEM, DEFAULT_VALUE_ITEM,
	     PROC_ITEM,COND_ITEM, REF_ITEM, FIELD_STD_ITEM,
	     FIELD_VARIANCE_ITEM, INSERT_VALUE_ITEM,
             SUBSELECT_ITEM, ROW_ITEM, CACHE_ITEM, TYPE_HOLDER,
             PARAM_ITEM, TRIGGER_FIELD_ITEM, DECIMAL_ITEM,
             XPATH_NODESET, XPATH_NODESET_CMP,
             VIEW_FIXER_ITEM};

  enum cond_result { COND_UNDEF,COND_OK,COND_TRUE,COND_FALSE };

  enum traverse_order { POSTFIX, PREFIX };
  
  /* Reuse size, only used by SP local variable assignment, otherwize 0 */
  uint rsize;

  /*
    str_values's main purpose is to be used to cache the value in
    save_in_field
  */
  String str_value;

  Item_name_string item_name;  /* Name from select */
  Item_name_string orig_name;  /* Original item name (if it was renamed)*/

  /**
     Intrusive list pointer for free list. If not null, points to the next
     Item on some Query_arena's free list. For instance, stored procedures
     have their own Query_arena's.

     @see Query_arena::free_list
   */
  Item *next;
  uint32 max_length;                    /* Maximum length, in bytes */
  /**
     This member has several successive meanings, depending on the phase we're
     in:
     - during field resolution: it contains the index, in the "all_fields"
     list, of the expression to which this field belongs; or a special
     constant UNDEF_POS; see st_select_lex::cur_pos_in_all_fields and
     match_exprs_for_only_full_group_by().
     - when attaching conditions to tables: it says whether some condition
     needs to be attached or can be omitted (for example because it is already
     implemented by 'ref' access)
     - when pushing index conditions: it says whether a condition uses only
     indexed columns
     - when creating an internal temporary table: it says how to store BIT
     fields
     - when we change DISTINCT to GROUP BY: it is used for book-keeping of
     fields.
  */
  int marker;
  uint8 decimals;
  my_bool maybe_null;			/* If item may be null */
  my_bool null_value;			/* if item is null */
  my_bool unsigned_flag;
  my_bool with_sum_func;
  my_bool fixed;                        /* If item fixed with fix_fields */
  DTCollation collation;
  Item_result cmp_context;              /* Comparison context */
  /*
    If this item was created in runtime memroot,it cannot be used for
    substitution in subquery transformation process
   */
  bool runtime_item;
 protected:
  my_bool with_subselect;               /* If this item is a subselect or some
                                           of its arguments is or contains a
                                           subselect. Computed by fix_fields
                                           and updated by update_used_tables. */
  my_bool with_stored_program;          /* If this item is a stored program
                                           or some of its arguments is or
                                           contains a stored program.
                                           Computed by fix_fields and updated
                                           by update_used_tables. */

  /**
    This variable is a cache of 'Needed tables are locked'. True if either
    'No tables locks is needed' or 'Needed tables are locked'.
    If tables are used, then it will be set to
    current_thd->lex->is_query_tables_locked().

    It is used when checking const_item()/can_be_evaluated_now().
  */
  bool tables_locked_cache;
 public:
  // alloc & destruct is done as start of select using sql_alloc
  Item();
  /*
     Constructor used by Item_field, Item_ref & aggregate (sum) functions.
     Used for duplicating lists in processing queries with temporary
     tables
     Also it used for Item_cond_and/Item_cond_or for creating
     top AND/OR structure of WHERE clause to protect it of
     optimisation changes in prepared statements
  */
  Item(THD *thd, Item *item);
  virtual ~Item()
  {
#ifdef EXTRA_DEBUG
    item_name.set(0);
#endif
  }		/*lint -e1509 */
  void rename(char *new_name);
  /*
    should be used in case where we are sure that we do not need
    complete fix_fields() procedure.
  */
  inline void quick_fix_field() { fixed= 1; }
  virtual Item_result result_type() const { return REAL_RESULT; }
  /**
    Result type when an item appear in a numeric context.
    See Field::numeric_context_result_type() for more comments.
  */
  virtual enum Item_result numeric_context_result_type() const
  {
    if (result_type() == STRING_RESULT)
      return REAL_RESULT; 
    return result_type();
  }
  virtual Item_result cast_to_int_type() const { return result_type(); }
  virtual enum_field_types string_field_type() const;
  virtual enum_field_types field_type() const;
  virtual enum Type type() const =0;
  
  /*
    Return information about function monotonicity. See comment for
    enum_monotonicity_info for details. This function can only be called
    after fix_fields() call.
  */
  virtual enum_monotonicity_info get_monotonicity_info() const
  { return NON_MONOTONIC; }

  /* valXXX methods must return NULL or 0 or 0.0 if null_value is set. */
  /*
    Return double precision floating point representation of item.

    SYNOPSIS
      val_real()

    RETURN
      In case of NULL value return 0.0 and set null_value flag to TRUE.
      If value is not null null_value flag will be reset to FALSE.
  */
  virtual double val_real()=0;
  /*
    Return integer representation of item.

    SYNOPSIS
      val_int()

    RETURN
      In case of NULL value return 0 and set null_value flag to TRUE.
      If value is not null null_value flag will be reset to FALSE.
  */
  virtual longlong val_int()=0;

  /*
    This is just a shortcut to avoid the cast. You should still use
    unsigned_flag to check the sign of the item.
  */
  inline ulonglong val_uint() { return (ulonglong) val_int(); }
  /*
    Return string representation of this item object.

    SYNOPSIS
      val_str()
      str   an allocated buffer this or any nested Item object can use to
            store return value of this method.

    NOTE
      Buffer passed via argument  should only be used if the item itself
      doesn't have an own String buffer. In case when the item maintains
      it's own string buffer, it's preferable to return it instead to
      minimize number of mallocs/memcpys.
      The caller of this method can modify returned string, but only in case
      when it was allocated on heap, (is_alloced() is true).  This allows
      the caller to efficiently use a buffer allocated by a child without
      having to allocate a buffer of it's own. The buffer, given to
      val_str() as argument, belongs to the caller and is later used by the
      caller at it's own choosing.
      A few implications from the above:
      - unless you return a string object which only points to your buffer
        but doesn't manages it you should be ready that it will be
        modified.
      - even for not allocated strings (is_alloced() == false) the caller
        can change charset (see Item_func_{typecast/binary}. XXX: is this
        a bug?
      - still you should try to minimize data copying and return internal
        object whenever possible.

    RETURN
      In case of NULL value return 0 (NULL pointer) and set null_value flag
      to TRUE.
      If value is not null null_value flag will be reset to FALSE.
  */
  virtual String *val_str(String *str)=0;

  /*
    Returns string representation of this item in ASCII format.

    SYNOPSIS
      val_str_ascii()
      str - similar to val_str();

    NOTE
      This method is introduced for performance optimization purposes.

      1. val_str() result of some Items in string context
      depends on @@character_set_results.
      @@character_set_results can be set to a "real multibyte" character
      set like UCS2, UTF16, UTF32. (We'll use only UTF32 in the examples
      below for convenience.)

      So the default string result of such functions
      in these circumstances is real multi-byte character set, like UTF32.

      For example, all numbers in string context
      return result in @@character_set_results:

      SELECT CONCAT(20010101); -> UTF32

      We do sprintf() first (to get ASCII representation)
      and then convert to UTF32;
      
      So these kind "data sources" can use ASCII representation
      internally, but return multi-byte data only because
      @@character_set_results wants so.
      Therefore, conversion from ASCII to UTF32 is applied internally.


      2. Some other functions need in fact ASCII input.

      For example,
        inet_aton(), GeometryFromText(), Convert_TZ(), GET_FORMAT().

      Similar, fields of certain type, like DATE, TIME,
      when you insert string data into them, expect in fact ASCII input.
      If they get non-ASCII input, for example UTF32, they
      convert input from UTF32 to ASCII, and then use ASCII
      representation to do further processing.


      3. Now imagine we pass result of a data source of the first type
         to a data destination of the second type.

      What happens
        a. data source converts data from ASCII to UTF32, because
           @@character_set_results wants so and passes the result to
           data destination.
        b. data destination gets UTF32 string.
        c. data destination converts UTF32 string to ASCII,
           because it needs ASCII representation to be able to handle data
           correctly.

      As a result we get two steps of unnecessary conversion:
      From ASCII to UTF32, then from UTF32 to ASCII.

      A better way to handle these situations is to pass ASCII
      representation directly from the source to the destination.

      This is why val_str_ascii() introduced.

    RETURN
      Similar to val_str()
  */
  virtual String *val_str_ascii(String *str);
  
  /*
    Return decimal representation of item with fixed point.

    SYNOPSIS
      val_decimal()
      decimal_buffer  buffer which can be used by Item for returning value
                      (but can be not)

    NOTE
      Returned value should not be changed if it is not the same which was
      passed via argument.

    RETURN
      Return pointer on my_decimal (it can be other then passed via argument)
        if value is not NULL (null_value flag will be reset to FALSE).
      In case of NULL value it return 0 pointer and set null_value flag
        to TRUE.
  */
  virtual my_decimal *val_decimal(my_decimal *decimal_buffer)= 0;
  /*
    Return boolean value of item.

    RETURN
      FALSE value is false or NULL
      TRUE value is true (not equal to 0)
  */
  virtual bool val_bool();
  virtual String *val_nodeset(String*) { return 0; }

protected:
  /* Helper functions, see item_sum.cc */
  String *val_string_from_real(String *str);
  String *val_string_from_int(String *str);
  String *val_string_from_decimal(String *str);
  my_decimal *val_decimal_from_real(my_decimal *decimal_value);
  my_decimal *val_decimal_from_int(my_decimal *decimal_value);
  my_decimal *val_decimal_from_string(my_decimal *decimal_value);
  longlong val_int_from_decimal();
  double val_real_from_decimal();

public:

  virtual const char *full_name() const
  {
    return item_name.is_set() ? item_name.ptr() : "???";
  }

  /* bit map of tables used by item */
  virtual table_map used_tables() const { return (table_map) 0L; }

  /*
    Return table map of tables that can't be NULL tables (tables that are
    used in a context where if they would contain a NULL row generated
    by a LEFT or RIGHT join, the item would not be true).
    This expression is used on WHERE item to determinate if a LEFT JOIN can be
    converted to a normal join.
    Generally this function should return used_tables() if the function
    would return null if any of the arguments are null
    As this is only used in the beginning of optimization, the value don't
    have to be updated in update_used_tables()
  */
  virtual table_map not_null_tables() const { return used_tables(); }
  /*
    Returns true if this is a simple constant item like an integer, not
    a constant expression. Used in the optimizer to propagate basic constants.
  */
  virtual bool basic_const_item() const { return 0; }
  /* cloning of constant items (0 if it is not const) */
  virtual cond_result eq_cmp_result() const { return COND_OK; }
  inline uint float_length(uint decimals_par) const
  { return decimals != NOT_FIXED_DEC ? (DBL_DIG+2+decimals_par) : DBL_DIG+8;}
  virtual uint decimal_precision() const;
  inline int decimal_int_part() const
  { return my_decimal_int_part(decimal_precision(), decimals); }
  /* 
    Returns true if this is constant (during query execution, i.e. its value
    will not change until next fix_fields) and its value is known.
    When the default implementation of used_tables() is effective, this
    function will always return true (because used_tables() is empty).
  */
  virtual bool const_item() const
  {
    if (used_tables() == 0)
      return can_be_evaluated_now();
    return false;
  }

  /**
    This method is used for to:
      - to generate a view definition query (SELECT-statement);
      - to generate a SQL-query for EXPLAIN EXTENDED;
      - to generate a SQL-query to be shown in INFORMATION_SCHEMA;
      - debug.

    For more information about view definition query, INFORMATION_SCHEMA
    query and why they should be generated from the Item-tree, @see
    mysql_register_view().
  */
  virtual inline void print(String *str, enum_query_type query_type)
  {
    str->append(full_name());
  }

  void print_item_w_name(String *, enum_query_type query_type);
  /**
     Prints the item when it's part of ORDER BY and GROUP BY.
     @param  str            String to print to
     @param  query_type     How to format the item
     @param  used_alias     Whether item was referenced with alias.
  */
  void print_for_order(String *str, enum_query_type query_type,
                       bool used_alias);


  /*
    The method allows to determine nullness of a complex expression 
    without fully evaluating it, instead of calling val/result*() then 
    checking null_value. Used in Item_func_isnull/Item_func_isnotnull
    and Item_sum_count/Item_sum_count_distinct.
    Any new item which can be NULL must implement this method.
  */
  virtual bool is_null() { return 0; }

  /*
    Inform the item that there will be no distinction between its result
    being FALSE or NULL.

    NOTE
      This function will be called for eg. Items that are top-level AND-parts
      of the WHERE clause. Items implementing this function (currently
      Item_cond_and and subquery-related item) enable special optimizations
      when they are "top level".
  */
  virtual void top_level_item() {}
  virtual bool is_result_field() { return 0; }
  virtual bool is_bool_func() { return 0; }
  virtual void save_in_result_field(bool no_conversions) {}

  virtual Item *real_item() { return this; }
  virtual Item *substitutional_item()
  {
    return  runtime_item ? real_item() : this;
  }
  virtual void set_runtime_created() { runtime_item= true; }

  static const CHARSET_INFO *default_charset();
  virtual const CHARSET_INFO *compare_collation() { return NULL; }

  /*
    For backward compatibility, to make numeric
    data types return "binary" charset in client-side metadata.
  */
  virtual const CHARSET_INFO *charset_for_protocol(void) const
  {
    return result_type() == STRING_RESULT ? collation.collation :
                                            &my_charset_bin;
  };

  virtual bool walk(Item_processor processor, bool walk_subquery, uchar *arg)
  {
    return (this->*processor)(arg);
  }

  /*
    This function performs a generic "compilation" of the Item tree.
    The process of compilation is assumed to go as follows: 
    
    compile()
    { 
      if (this->*some_analyzer(...))
      {
        compile children if any;
        return this->*some_transformer(...);
      }
      else
        return this;
    }

    i.e. analysis is performed top-down while transformation is done
    bottom-up. If no transformation is applied, the item is returned unchanged.
    A transformation error is indicated by returning a NULL pointer. Notice
    that the analyzer function should never cause an error.
  */
  virtual Item* compile(Item_analyzer analyzer, uchar **arg_p,
                        Item_transformer transformer, uchar *arg_t)
  {
    if ((this->*analyzer) (arg_p))
      return ((this->*transformer) (arg_t));
    return this;
  }

   virtual void traverse_cond(Cond_traverser traverser,
                              void *arg, traverse_order order)
   {
     (*traverser)(this, arg);
   }

  /*
    This is used to get the most recent version of any function in
    an item tree. The version is the version where a MySQL function
    was introduced in. So any function which is added should use
    this function and set the int_arg to maximum of the input data
    and their own version info.
  */
  virtual bool intro_version(uchar *int_arg) { return 0; }

  /**
     Analyzer for finding Item_field by name
     
     @param arg  Field name to search for
     
     @return TRUE Go deeper in item tree.  (Found Item or not an Item_field)
     @return FALSE Don't go deeper in item tree. (Item_field with other name)
  */
  virtual bool item_field_by_name_analyzer(uchar **arg) { return true; };

  /**
     Simple transformer that returns the argument if this is an Item_field.
     The new item will inherit it's name to maintain aliases.

     @param arg Item to replace Item_field

     @return argument if this is an Item_field
     @return this otherwise.
  */
  virtual Item* item_field_by_name_transformer(uchar *arg) { return this; }

  virtual bool equality_substitution_analyzer(uchar **arg) { return false; }

  virtual Item* equality_substitution_transformer(uchar *arg) { return this; }

  /*
    Check if a partition function is allowed
    SYNOPSIS
      check_partition_func_processor()
      int_arg                        Ignored
    RETURN VALUE
      TRUE                           Partition function not accepted
      FALSE                          Partition function accepted

    DESCRIPTION
    check_partition_func_processor is used to check if a partition function
    uses an allowed function. An allowed function will always ensure that
    X=Y guarantees that also part_function(X)=part_function(Y) where X is
    a set of partition fields and so is Y. The problems comes mainly from
    character sets where two equal strings can be quite unequal. E.g. the
    german character for double s is equal to 2 s.

    The default is that an item is not allowed
    in a partition function. Allowed functions
    can never depend on server version, they cannot depend on anything
    related to the environment. They can also only depend on a set of
    fields in the table itself. They cannot depend on other tables and
    cannot contain any queries and cannot contain udf's or similar.
    If a new Item class is defined and it inherits from a class that is
    allowed in a partition function then it is very important to consider
    whether this should be inherited to the new class. If not the function
    below should be defined in the new Item class.

    The general behaviour is that most integer functions are allowed.
    If the partition function contains any multi-byte collations then
    the function check_part_func_fields will report an error on the
    partition function independent of what functions are used. So the
    only character sets allowed are single character collation and
    even for those only a limited set of functions are allowed. The
    problem with multi-byte collations is that almost every string
    function has the ability to change things such that two strings
    that are equal will not be equal after manipulated by a string
    function. E.g. two strings one contains a double s, there is a
    special german character that is equal to two s. Now assume a
    string function removes one character at this place, then in
    one the double s will be removed and in the other there will
    still be one s remaining and the strings are no longer equal
    and thus the partition function will not sort equal strings into
    the same partitions.

    So the check if a partition function is valid is two steps. First
    check that the field types are valid, next check that the partition
    function is valid. The current set of partition functions valid
    assumes that there are no multi-byte collations amongst the partition
    fields.
  */
  virtual bool check_partition_func_processor(uchar *bool_arg) { return TRUE;}
  virtual bool subst_argument_checker(uchar **arg)
  { 
    if (*arg)
      *arg= NULL; 
    return TRUE;     
  }
  virtual bool explain_subquery_checker(uchar **arg) { return true; }
  virtual Item *explain_subquery_propagator(uchar *arg) { return this; }

  virtual Item *equal_fields_propagator(uchar * arg) { return this; }
  virtual bool set_no_const_sub(uchar *arg) { return FALSE; }
  virtual Item *replace_equal_field(uchar * arg) { return this; }
  /*
    Check if an expression value has allowed arguments, like DATE/DATETIME
    for date functions. Also used by partitioning code to reject
    timezone-dependent expressions in a (sub)partitioning function.
  */
  virtual bool check_valid_arguments_processor(uchar *bool_arg)
  {
    return FALSE;
  }

  /**
    Find a function of a given type

    @param   arg     the function type to search (enum Item_func::Functype)
    @return
      @retval TRUE   the function type we're searching for is found
      @retval FALSE  the function type wasn't found

    @description
      This function can be used (together with Item::walk()) to find functions
      in an item tree fragment.
  */
  virtual bool find_function_processor (uchar *arg)
  {
    return FALSE;
  }

  /*
    For SP local variable returns pointer to Item representing its
    current value and pointer to current Item otherwise.
  */
  virtual Item *this_item() { return this; }
  virtual const Item *this_item() const { return this; }

  /*
    For SP local variable returns address of pointer to Item representing its
    current value and pointer passed via parameter otherwise.
  */
  virtual Item **this_item_addr(THD *thd, Item **addr_arg) { return addr_arg; }

  // Row emulation
  virtual uint cols() { return 1; }
  virtual Item* element_index(uint i) { return this; }
  virtual Item** addr(uint i) { return 0; }
  virtual bool check_cols(uint c);
  // It is not row => null inside is impossible
  virtual bool null_inside() { return 0; }
  // used in row subselects to get value of elements
  virtual void bring_value() {}

  virtual Item_field *field_for_view_update() { return 0; }

  virtual Item *neg_transformer(THD *thd) { return NULL; }
  void delete_self()
  {
    delete this;
  }

  virtual bool is_splocal() { return 0; } /* Needed for error checking */

  /*
    Return Settable_routine_parameter interface of the Item.  Return 0
    if this Item is not Settable_routine_parameter.
  */
  virtual Settable_routine_parameter *get_settable_routine_parameter()
  {
    return 0;
  }
  inline bool is_temporal() const
  {
    return is_temporal_type(field_type());
  }

  String *check_well_formed_result(String *str, bool send_error= 0);

  /*
    Test whether an expression is expensive to compute. Used during
    optimization to avoid computing expensive expressions during this
    phase. Also used to force temp tables when sorting on expensive
    functions.
    TODO:
    Normally we should have a method:
      cost Item::execution_cost(),
    where 'cost' is either 'double' or some structure of various cost
    parameters.
  */
  virtual bool is_expensive()
  {
    if (is_expensive_cache < 0)
      is_expensive_cache= walk(&Item::is_expensive_processor, 0, (uchar*)0);
    return MY_TEST(is_expensive_cache);
  }
  virtual bool can_be_evaluated_now() const;
  uint32 max_char_length() const
  { return max_length / collation.collation->mbmaxlen; }
  void fix_length_and_charset(uint32 max_char_length_arg,
                              const CHARSET_INFO *cs)
  {
    max_length= char_to_byte_length_safe(max_char_length_arg, cs->mbmaxlen);
    collation.collation= cs;
  }
  void fix_char_length(uint32 max_char_length_arg)
  {
    max_length= char_to_byte_length_safe(max_char_length_arg,
                                         collation.collation->mbmaxlen);
  }
  void fix_char_length_ulonglong(ulonglong max_char_length_arg)
  {
    ulonglong max_result_length= max_char_length_arg *
                                 collation.collation->mbmaxlen;
    if (max_result_length >= MAX_BLOB_WIDTH)
    {
      max_length= MAX_BLOB_WIDTH;
      maybe_null= 1;
    }
    else
      max_length= (uint32) max_result_length;
  }
  void fix_length_and_charset_datetime(uint32 max_char_length_arg)
  {
    collation.set(&my_charset_numeric, DERIVATION_NUMERIC, MY_REPERTOIRE_ASCII);
    fix_char_length(max_char_length_arg);
  }
  void fix_length_and_dec_and_charset_datetime(uint32 max_char_length_arg,
                                               uint8 dec_arg)
  {
    decimals= dec_arg;
    fix_length_and_charset_datetime(max_char_length_arg +
                                    (dec_arg ? dec_arg + 1 : 0));
  }
  /*
    Return TRUE if the item points to a column of an outer-joined table.
  */
  virtual bool is_outer_field() const { DBUG_ASSERT(fixed); return FALSE; }

  /**
     Check if an item either is a blob field, or will be represented as a BLOB
     field if a field is created based on this item.

     @retval TRUE  If a field based on this item will be a BLOB field,
     @retval FALSE Otherwise.
  */
  bool is_blob_field() const;

  /**
    Checks if this item or any of its decendents contains a subquery.
  */
  virtual bool has_subquery() const { return with_subselect; }
  virtual bool has_stored_program() const { return with_stored_program; }
  /// Whether this Item was created by the IN->EXISTS subquery transformation
  virtual bool created_by_in2exists() const { return false; }
};


class sp_head;


class Item_basic_constant :public Item
{
  table_map used_table_map;
public:
  Item_basic_constant(): Item(), used_table_map(0) {};
  void set_used_tables(table_map map) { used_table_map= map; }
  table_map used_tables() const { return used_table_map; }
};


/*****************************************************************************
  The class is a base class for representation of stored routine variables in
  the Item-hierarchy. There are the following kinds of SP-vars:
    - local variables (Item_splocal);
    - CASE expression (Item_case_expr);
*****************************************************************************/

class Item_sp_variable :public Item
{
protected:
  /*
    THD, which is stored in fix_fields() and is used in this_item() to avoid
    current_thd use.
  */
  THD *m_thd;

public:
  Name_string m_name;

public:
#ifndef DBUG_OFF
  /*
    Routine to which this Item_splocal belongs. Used for checking if correct
    runtime context is used for variable handling.
  */
  sp_head *m_sp;
#endif

public:
  Item_sp_variable(const Name_string sp_var_name);

  double val_real();
  longlong val_int();
  String *val_str(String *sp);
  my_decimal *val_decimal(my_decimal *decimal_value);
  bool is_null();
};


/*****************************************************************************
  A reference to local SP variable (incl. reference to SP parameter), used in
  runtime.
*****************************************************************************/

class Item_splocal :public Item_sp_variable,
                    private Settable_routine_parameter
{
  uint m_var_idx;

  Type m_type;
  Item_result m_result_type;
  enum_field_types m_field_type;
public:
  /*
    If this variable is a parameter in LIMIT clause.
    Used only during NAME_CONST substitution, to not append
    NAME_CONST to the resulting query and thus not break
    the slave.
  */
  bool limit_clause_param;
  /* 
    Position of this reference to SP variable in the statement (the
    statement itself is in sp_instr_stmt::m_query).
    This is valid only for references to SP variables in statements,
    excluding DECLARE CURSOR statement. It is used to replace references to SP
    variables with NAME_CONST calls when putting statements into the binary
    log.
    Value of 0 means that this object doesn't corresponding to reference to
    SP variable in query text.
  */
  uint pos_in_query;
  /*
    Byte length of SP variable name in the statement (see pos_in_query).
    The value of this field may differ from the name_length value because
    name_length contains byte length of UTF8-encoded item name, but
    the query string (see sp_instr_stmt::m_query) is currently stored with
    a charset from the SET NAMES statement.
  */
  uint len_in_query;

  Item_splocal(const Name_string sp_var_name, uint sp_var_idx,
               enum_field_types sp_var_type,
               uint pos_in_q= 0, uint len_in_q= 0);

  bool is_splocal() { return 1; } /* Needed for error checking */

  virtual void print(String *str, enum_query_type query_type);

public:
  inline uint get_var_idx() const;

  inline enum Type type() const;
  inline Item_result result_type() const;
  inline enum_field_types field_type() const { return m_field_type; }

private:
  bool set_value(THD *thd, sp_rcontext *ctx, Item **it);

public:
  Settable_routine_parameter *get_settable_routine_parameter()
  {
    return this;
  }
};

/*****************************************************************************
  Item_splocal inline implementation.
*****************************************************************************/

inline uint Item_splocal::get_var_idx() const
{
  return m_var_idx;
}

inline enum Item::Type Item_splocal::type() const
{
  return m_type;
}

inline Item_result Item_splocal::result_type() const
{
  return m_result_type;
}


/*****************************************************************************
  A reference to case expression in SP, used in runtime.
*****************************************************************************/

class Item_case_expr :public Item_sp_variable
{
public:
  Item_case_expr(uint case_expr_id);

public:
  inline enum Type type() const;
  inline Item_result result_type() const;

public:
  /*
    NOTE: print() is intended to be used from views and for debug.
    Item_case_expr can not occur in views, so here it is only for debug
    purposes.
  */
  virtual void print(String *str, enum_query_type query_type);

private:
  uint m_case_expr_id;
};

/*****************************************************************************
  Item_case_expr inline implementation.
*****************************************************************************/

inline enum Item::Type Item_case_expr::type() const
{
  return this_item()->type();
}

inline Item_result Item_case_expr::result_type() const
{
  return this_item()->result_type();
}


/*
  NAME_CONST(given_name, const_value). 
  This 'function' has all properties of the supplied const_value (which is 
  assumed to be a literal constant), and the name given_name. 

  This is used to replace references to SP variables when we write PROCEDURE
  statements into the binary log.

  TODO
    Together with Item_splocal and Item::this_item() we can actually extract
    common a base of this class and Item_splocal. Maybe it is possible to
    extract a common base with class Item_ref, too.
*/

class Item_name_const : public Item
{
  Item *value_item;
  Item *name_item;
  bool valid_args;
public:
  Item_name_const(Item *name_arg, Item *val);

  enum Type type() const;
  double val_real();
  longlong val_int();
  String *val_str(String *sp);
  my_decimal *val_decimal(my_decimal *);
  bool is_null();
  virtual void print(String *str, enum_query_type query_type);

  Item_result result_type() const
  {
    return value_item->result_type();
  }
};

bool agg_item_collations(DTCollation &c, const char *name,
                         Item **items, uint nitems, uint flags, int item_sep);
bool agg_item_collations_for_comparison(DTCollation &c, const char *name,
                                        Item **items, uint nitems, uint flags);

class Item_num: public Item_basic_constant
{
public:
  Item_num() { collation.set_numeric(); } /* Remove gcc warning */
  virtual Item_num *neg()= 0;
  bool check_partition_func_processor(uchar *int_arg) { return FALSE;}
};

#define NO_CACHED_FIELD_INDEX ((uint)(-1))

class st_select_lex;
class Item_ident :public Item
{
protected:
  /* 
    We have to store initial values of db_name, table_name and field_name
    to be able to restore them during cleanup() because they can be 
    updated during fix_fields() to values from Field object and life-time 
    of those is shorter than life-time of Item_field.
  */
  const char *orig_db_name;
  const char *orig_table_name;
  const char *orig_field_name;

public:
  Name_resolution_context *context;
  const char *db_name;
  const char *table_name;
  const char *field_name;
  bool alias_name_used; /* true if item was resolved against alias */
  /* 
    Cached value of index for this field in table->field array, used by prep. 
    stmts for speeding up their re-execution. Holds NO_CACHED_FIELD_INDEX 
    if index value is not known.
  */
  uint cached_field_index;
  /*
    Cached pointer to table which contains this field, used for the same reason
    by prep. stmt. too in case then we have not-fully qualified field.
    0 - means no cached value.
  */
  TABLE_LIST *cached_table;
  st_select_lex *depended_from;
  Item_ident(Name_resolution_context *context_arg,
             const char *db_name_arg, const char *table_name_arg,
             const char *field_name_arg);
  Item_ident(THD *thd, Item_ident *item);
  const char *full_name() const;
  virtual void print(String *str, enum_query_type query_type);
  virtual bool change_context_processor(uchar *cntx)
    { context= (Name_resolution_context *)cntx; return FALSE; }
};



class Item_equal;
class COND_EQUAL;

class Item_field :public Item_ident
{
public:
  Item_equal *item_equal;
  bool no_const_subst;
  /*
    if any_privileges set to TRUE then here real effective privileges will
    be stored
  */
  uint have_privileges;
  /* field need any privileges (for VIEW creation) */
  bool any_privileges;
  Item_field(Name_resolution_context *context_arg,
             const char *db_arg,const char *table_name_arg,
	     const char *field_name_arg);
  /*
    Constructor needed to process subquery with temporary tables (see Item).
    Notice that it will have no name resolution context.
  */
  Item_field(THD *thd, Item_field *item);
  enum Type type() const { return FIELD_ITEM; }

  double val_real() {return 0.0;}
  longlong val_int() {return 0;}

  my_decimal *val_decimal(my_decimal *) {return NULL;}
  String *val_str(String*) {return NULL;}
  enum_monotonicity_info get_monotonicity_info() const
  {
    return MONOTONIC_STRICT_INCREASING;
  }
  Item_field *field_for_view_update() { return this; }

  virtual void print(String *str, enum_query_type query_type);

  friend class Item_default_value;
  friend class Item_insert_value;
  friend class st_select_lex_unit;
};

class Item_null :public Item_basic_constant
{
  void init()
  {
    maybe_null= null_value= TRUE;
    max_length= 0;
    fixed= 1;
    collation.set(&my_charset_bin, DERIVATION_IGNORABLE);
  }
public:
  Item_null()
  {
    init();
    item_name= NAME_STRING("NULL");
  }
  Item_null(const Name_string &name_par)
  {
    init();
    item_name= name_par;
  }
  enum Type type() const { return NULL_ITEM; }
  double val_real();
  longlong val_int();
  String *val_str(String *str);
  my_decimal *val_decimal(my_decimal *);
  bool send(Protocol *protocol, String *str);
  enum Item_result result_type () const { return STRING_RESULT; }
  enum_field_types field_type() const   { return MYSQL_TYPE_NULL; }
  bool basic_const_item() const { return 1; }
  bool is_null() { return 1; }

  virtual inline void print(String *str, enum_query_type query_type)
  {
    str->append(STRING_WITH_LEN("NULL"));
  }

  bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
};

/**
  An item representing NULL values for use with ROLLUP.

  When grouping WITH ROLLUP, Item_null_result items are created to
  represent NULL values in the grouping columns of the ROLLUP rows. To
  avoid type problems during execution, these objects are created with
  the same field and result types as the fields of the columns they
  belong to.
 */
class Item_null_result :public Item_null
{
  /** Field type for this NULL value */
  enum_field_types fld_type;
  /** Result type for this NULL value */
  Item_result res_type;

public:
  bool check_partition_func_processor(uchar *int_arg) {return TRUE;}
  enum_field_types field_type() const { return fld_type; }
  Item_result result_type() const { return res_type; }
};  

/* Item represents one placeholder ('?') of prepared statement */

class Item_param :public Item,
                  private Settable_routine_parameter
{
  char cnvbuf[MAX_FIELD_WIDTH];
  String cnvstr;
  Item *cnvitem;

public:
  enum enum_item_param_state
  {
    NO_VALUE, NULL_VALUE, INT_VALUE, REAL_VALUE,
    STRING_VALUE, TIME_VALUE, LONG_DATA_VALUE,
    DECIMAL_VALUE
  } state;

  /*
    A buffer for string and long data values. Historically all allocated
    values returned from val_str() were treated as eligible to
    modification. I. e. in some cases Item_func_concat can append it's
    second argument to return value of the first one. Because of that we
    can't return the original buffer holding string data from val_str(),
    and have to have one buffer for data and another just pointing to
    the data. This is the latter one and it's returned from val_str().
    Can not be declared inside the union as it's not a POD type.
  */
  String str_value_ptr;
  my_decimal decimal_value;
  union
  {
    longlong integer;
    double   real;
    /*
      Character sets conversion info for string values.
      Character sets of client and connection defined at bind time are used
      for all conversions, even if one of them is later changed (i.e.
      between subsequent calls to mysql_stmt_execute).
    */
    struct CONVERSION_INFO
    {
      const CHARSET_INFO *character_set_client;
      const CHARSET_INFO *character_set_of_placeholder;
      /*
        This points at character set of connection if conversion
        to it is required (i. e. if placeholder typecode is not BLOB).
        Otherwise it's equal to character_set_client (to simplify
        check in convert_str_value()).
      */
      const CHARSET_INFO *final_character_set_of_str_value;
    } cs_info;
    MYSQL_TIME     time;
  } value;

  /* Cached values for virtual methods to save us one switch.  */
  enum Item_result item_result_type;
  enum Type item_type;

  /*
    Used when this item is used in a temporary table.
    This is NOT placeholder metadata sent to client, as this value
    is assigned after sending metadata (in setup_one_conversion_function).
    For example in case of 'SELECT ?' you'll get MYSQL_TYPE_STRING both
    in result set and placeholders metadata, no matter what type you will
    supply for this placeholder in mysql_stmt_execute.
  */
  enum enum_field_types param_type;
  /*
    Offset of placeholder inside statement text. Used to create
    no-placeholders version of this statement for the binary log.
  */
  uint pos_in_query;

  Item_param(uint pos_in_query_arg);

  enum Item_result result_type () const { return item_result_type; }
  enum Type type() const { return item_type; }
  enum_field_types field_type() const { return param_type; }

  double val_real();
  longlong val_int();
  my_decimal *val_decimal(my_decimal*);
  String *val_str(String*);

  void set_null();
  void set_int(longlong i, uint32 max_length_arg);
  void set_double(double i);
  void set_decimal(const char *str, ulong length);
  void set_decimal(const my_decimal *dv);
  bool set_str(const char *str, ulong length);
  bool set_longdata(const char *str, ulong length);
  void set_time(MYSQL_TIME *tm, timestamp_type type, uint32 max_length_arg);
  bool set_from_user_var(THD *thd, const user_var_entry *entry);
  void reset();
  /*
    Assign placeholder value from bind data.
    Note, that 'len' has different semantics in embedded library (as we
    don't need to check that packet is not broken there). See
    sql_prepare.cc for details.
  */
  void (*set_param_func)(Item_param *param, uchar **pos, ulong len);

  const String *query_val_str(THD *thd, String *str) const;

  bool convert_str_value(THD *thd);

  /*
    If value for parameter was not set we treat it as non-const
    so noone will use parameters value in fix_fields still
    parameter is constant during execution.
  */
  virtual table_map used_tables() const
  { return state != NO_VALUE ? (table_map)0 : PARAM_TABLE_BIT; }
  virtual void print(String *str, enum_query_type query_type);
  bool is_null()
  { DBUG_ASSERT(state != NO_VALUE); return state == NULL_VALUE; }
  bool basic_const_item() const;
  /** Item is a argument to a limit clause. */
  bool limit_clause_param;
  void set_param_type_and_swap_value(Item_param *from);

private:
  virtual inline Settable_routine_parameter *
    get_settable_routine_parameter()
  {
    return this;
  }
};


class Item_int :public Item_num
{
public:
  longlong value;
  Item_int(int32 i,uint length= MY_INT32_NUM_DECIMAL_DIGITS)
    :value((longlong) i)
    { max_length=length; fixed= 1; }
  Item_int(longlong i,uint length= MY_INT64_NUM_DECIMAL_DIGITS)
    :value(i)
    { max_length=length; fixed= 1; }
  Item_int(ulonglong i, uint length= MY_INT64_NUM_DECIMAL_DIGITS)
    :value((longlong)i)
    { max_length=length; fixed= 1; unsigned_flag= 1; }
  Item_int(Item_int *item_arg)
  {
    value= item_arg->value;
    item_name= item_arg->item_name;
    max_length= item_arg->max_length;
    fixed= 1;
  }
  Item_int(const Name_string &name_arg, longlong i, uint length) :value(i)
  {
    max_length= length;
    item_name= name_arg;
    fixed= 1;
  }
  Item_int(const char *str_arg, uint length);
  enum Type type() const { return INT_ITEM; }
  enum Item_result result_type () const { return INT_RESULT; }
  enum_field_types field_type() const { return MYSQL_TYPE_LONGLONG; }
  longlong val_int() { DBUG_ASSERT(fixed == 1); return value; }
  double val_real() { DBUG_ASSERT(fixed == 1); return (double) value; }
  my_decimal *val_decimal(my_decimal *);
  String *val_str(String*);
  bool basic_const_item() const { return 1; }
  virtual void print(String *str, enum_query_type query_type);
  Item_num *neg() { value= -value; return this; }
  uint decimal_precision() const
  { return (uint)(max_length - MY_TEST(value < 0)); }
  bool check_partition_func_processor(uchar *bool_arg) { return FALSE;}
};


/**
  Item_int with value==0 and length==1
*/
class Item_int_0 :public Item_int
{
public:
  Item_int_0() :Item_int(NAME_STRING("0"), 0, 1) {}
};


class Item_uint :public Item_int
{
public:
  Item_uint(const char *str_arg, uint length)
    :Item_int(str_arg, length) { unsigned_flag= 1; }
  Item_uint(ulonglong i) :Item_int((ulonglong) i, 10) {}
  Item_uint(const Name_string &name_arg, longlong i, uint length)
    :Item_int(name_arg, i, length) { unsigned_flag= 1; }
  double val_real()
    { DBUG_ASSERT(fixed == 1); return ulonglong2double((ulonglong)value); }
  String *val_str(String*);

  virtual void print(String *str, enum_query_type query_type);
  Item_num *neg ();
  uint decimal_precision() const { return max_length; }
  bool check_partition_func_processor(uchar *bool_arg) { return FALSE;}
};


/* decimal (fixed point) constant */
class Item_decimal :public Item_num
{
protected:
  my_decimal decimal_value;
public:
  Item_decimal(const char *str_arg, uint length, const CHARSET_INFO *charset);
  Item_decimal(const Name_string &name_arg,
               const my_decimal *val_arg, uint decimal_par, uint length);
  Item_decimal(my_decimal *value_par);
  Item_decimal(longlong val, bool unsig);
  Item_decimal(double val, int precision, int scale);
  Item_decimal(const uchar *bin, int precision, int scale);

  enum Type type() const { return DECIMAL_ITEM; }
  enum Item_result result_type () const { return DECIMAL_RESULT; }
  enum_field_types field_type() const { return MYSQL_TYPE_NEWDECIMAL; }
  longlong val_int();
  double val_real();
  String *val_str(String*);
  my_decimal *val_decimal(my_decimal *val) { return &decimal_value; }
  bool basic_const_item() const { return 1; }
  virtual void print(String *str, enum_query_type query_type);
  Item_num *neg()
  {
    my_decimal_neg(&decimal_value);
    unsigned_flag= !decimal_value.sign();
    return this;
  }
  uint decimal_precision() const { return decimal_value.precision(); }
  void set_decimal_value(my_decimal *value_par);
  bool check_partition_func_processor(uchar *bool_arg) { return FALSE;}
};


class Item_float :public Item_num
{
  Name_string presentation;
public:
  double value;
  // Item_real() :value(0) {}
  Item_float(const char *str_arg, uint length);
  Item_float(const Name_string name_arg,
             double val_arg, uint decimal_par, uint length)
    :value(val_arg)
  {
    presentation= name_arg;
    item_name= name_arg;
    decimals= (uint8) decimal_par;
    max_length= length;
    fixed= 1;
  }
  Item_float(double value_par, uint decimal_par) :value(value_par)
  {
    decimals= (uint8) decimal_par;
    fixed= 1;
  }
  enum Type type() const { return REAL_ITEM; }
  enum_field_types field_type() const { return MYSQL_TYPE_DOUBLE; }
  double val_real() { DBUG_ASSERT(fixed == 1); return value; }
  longlong val_int()
  {
    DBUG_ASSERT(fixed == 1);
    if (value <= (double) LONGLONG_MIN)
    {
       return LONGLONG_MIN;
    }
    else if (value >= (double) (ulonglong) LONGLONG_MAX)
    {
      return LONGLONG_MAX;
    }
    return (longlong) rint(value);
  }
  String *val_str(String*);
  my_decimal *val_decimal(my_decimal *);
  bool basic_const_item() const { return 1; }
  Item_num *neg() { value= -value; return this; }
  virtual void print(String *str, enum_query_type query_type);
};


class Item_static_float_func :public Item_float
{
  const Name_string func_name;
public:
  Item_static_float_func(const Name_string &name_arg,
                         double val_arg, uint decimal_par, uint length)
    :Item_float(null_name_string,
                val_arg, decimal_par, length), func_name(name_arg)
  {}

  virtual inline void print(String *str, enum_query_type query_type)
  {
    str->append(func_name);
  }
};


class Item_string :public Item_basic_constant
{
public:
  /* Create from a string, set name from the string itself. */
  Item_string(const char *str,uint length,
              const CHARSET_INFO *cs, Derivation dv= DERIVATION_COERCIBLE,
              uint repertoire= MY_REPERTOIRE_UNICODE30)
    : m_cs_specified(FALSE)
  {
    str_value.set_or_copy_aligned(str, length, cs);
    collation.set(cs, dv, repertoire);
    /*
      We have to have a different max_length than 'length' here to
      ensure that we get the right length if we do use the item
      to create a new table. In this case max_length must be the maximum
      number of chars for a string of this type because we in Create_field::
      divide the max_length with mbmaxlen).
    */
    max_length= str_value.numchars()*cs->mbmaxlen;
    item_name.copy(str, length, cs);
    decimals=NOT_FIXED_DEC;
    // it is constant => can be used without fix_fields (and frequently used)
    fixed= 1;
  }
  /* Just create an item and do not fill string representation */
  Item_string(const CHARSET_INFO *cs, Derivation dv= DERIVATION_COERCIBLE)
    : m_cs_specified(FALSE)
  {
    collation.set(cs, dv);
    max_length= 0;
    decimals= NOT_FIXED_DEC;
    fixed= 1;
  }
  /* Create from the given name and string. */
  Item_string(const Name_string name_par, const char *str, uint length,
              const CHARSET_INFO *cs, Derivation dv= DERIVATION_COERCIBLE,
              uint repertoire= MY_REPERTOIRE_UNICODE30)
    : m_cs_specified(FALSE)
  {
    str_value.set_or_copy_aligned(str, length, cs);
    collation.set(cs, dv, repertoire);
    max_length= str_value.numchars()*cs->mbmaxlen;
    item_name= name_par;
    decimals=NOT_FIXED_DEC;
    // it is constant => can be used without fix_fields (and frequently used)
    fixed= 1;
  }
  /*
    This is used in stored procedures to avoid memory leaks and
    does a deep copy of its argument.
  */
  void set_str_with_copy(const char *str_arg, uint length_arg)
  {
    str_value.copy(str_arg, length_arg, collation.collation);
    max_length= str_value.numchars() * collation.collation->mbmaxlen;
  }
  void set_repertoire_from_value()
  {
    collation.repertoire= my_string_repertoire(str_value.charset(),
                                               str_value.ptr(),
                                               str_value.length());
  }
  enum Type type() const { return STRING_ITEM; }
  double val_real();
  longlong val_int();
  String *val_str(String*)
  {
    DBUG_ASSERT(fixed == 1);
    return (String*) &str_value;
  }
  my_decimal *val_decimal(my_decimal *);
  enum Item_result result_type () const { return STRING_RESULT; }
  enum_field_types field_type() const { return MYSQL_TYPE_VARCHAR; }
  bool basic_const_item() const { return 1; }

  inline void append(char *str, uint length)
  {
    str_value.append(str, length);
    max_length= str_value.numchars() * collation.collation->mbmaxlen;
  }
  virtual void print(String *str, enum_query_type query_type);
  bool check_partition_func_processor(uchar *int_arg) {return FALSE;}

  /**
    Return TRUE if character-set-introducer was explicitly specified in the
    original query for this item (text literal).

    This operation is to be called from Item_string::print(). The idea is
    that when a query is generated (re-constructed) from the Item-tree,
    character-set-introducers should appear only for those literals, where
    they were explicitly specified by the user. Otherwise, that may lead to
    loss collation information (character set introducers implies default
    collation for the literal).

    Basically, that makes sense only for views and hopefully will be gone
    one day when we start using original query as a view definition.

    @return This operation returns the value of m_cs_specified attribute.
      @retval TRUE if character set introducer was explicitly specified in
      the original query.
      @retval FALSE otherwise.
  */
  inline bool is_cs_specified() const
  {
    return m_cs_specified;
  }

  /**
    Set the value of m_cs_specified attribute.

    m_cs_specified attribute shows whether character-set-introducer was
    explicitly specified in the original query for this text literal or
    not. The attribute makes sense (is used) only for views.

    This operation is to be called from the parser during parsing an input
    query.
  */
  inline void set_cs_specified(bool cs_specified)
  {
    m_cs_specified= cs_specified;
  }

private:
  bool m_cs_specified;
};


longlong 
longlong_from_string_with_check (const CHARSET_INFO *cs,
                                 const char *cptr, char *end);
double 
double_from_string_with_check (const CHARSET_INFO *cs,
                               const char *cptr, char *end);

class Item_static_string_func :public Item_string
{
  const Name_string func_name;
public:
  Item_static_string_func(const Name_string &name_par,
                          const char *str, uint length, const CHARSET_INFO *cs,
                          Derivation dv= DERIVATION_COERCIBLE)
    :Item_string(null_name_string, str, length, cs, dv), func_name(name_par)
  {}

  virtual inline void print(String *str, enum_query_type query_type)
  {
    str->append(func_name);
  }

  bool check_partition_func_processor(uchar *int_arg) {return TRUE;}
};


/* for show tables */
class Item_partition_func_safe_string: public Item_string
{
public:
  Item_partition_func_safe_string(const Name_string name, uint length,
                                  const CHARSET_INFO *cs= NULL):
    Item_string(name, NullS, 0, cs)
  {
    max_length= length;
  }
};


class Item_blob :public Item_partition_func_safe_string
{
public:
  Item_blob(const char *name, uint length) :
    Item_partition_func_safe_string(Name_string(name, strlen(name)),
                                    length, &my_charset_bin)
  { }
  enum Type type() const { return TYPE_HOLDER; }
  enum_field_types field_type() const { return MYSQL_TYPE_BLOB; }
};


/**
  Item_empty_string -- is a utility class to put an item into List<Item>
  which is then used in protocol.send_result_set_metadata() when sending SHOW output to
  the client.
*/

class Item_empty_string :public Item_partition_func_safe_string
{
public:
  Item_empty_string(const char *header, uint length,
                    const CHARSET_INFO *cs= NULL) :
    Item_partition_func_safe_string(Name_string(header, strlen(header)),
                                    0, cs ? cs : &my_charset_utf8_general_ci)
    {
      max_length= length * collation.collation->mbmaxlen;
    }
};


class Item_return_int :public Item_int
{
  enum_field_types int_field_type;
public:
  Item_return_int(const char *name_arg, uint length,
		  enum_field_types field_type_arg, longlong value= 0)
    :Item_int(Name_string(name_arg, name_arg ? strlen(name_arg) : 0),
              value, length), int_field_type(field_type_arg)
  {
    unsigned_flag=1;
  }
  enum_field_types field_type() const { return int_field_type; }
};


class Item_hex_string: public Item_basic_constant
{
public:
  Item_hex_string();
  Item_hex_string(const char *str,uint str_length);
  enum Type type() const { return VARBIN_ITEM; }
  double val_real()
  { 
    DBUG_ASSERT(fixed == 1); 
    return (double) (ulonglong) Item_hex_string::val_int();
  }
  longlong val_int();
  bool basic_const_item() const { return 1; }
  String *val_str(String*) { DBUG_ASSERT(fixed == 1); return &str_value; }
  my_decimal *val_decimal(my_decimal *);
  enum Item_result result_type () const { return STRING_RESULT; }
  enum Item_result cast_to_int_type() const { return INT_RESULT; }
  enum_field_types field_type() const { return MYSQL_TYPE_VARCHAR; }
  virtual void print(String *str, enum_query_type query_type);
  bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
private:
  void hex_string_init(const char *str, uint str_length);
};


class Item_bin_string: public Item_hex_string
{
public:
  Item_bin_string(const char *str,uint str_length);
};


class Item_result_field :public Item	/* Item with result field */
{
public:
  /*
    This method is used for debug purposes to print the name of an
    item to the debug log. The second use of this method is as
    a helper function of print() and error messages, where it is
    applicable. To suit both goals it should return a meaningful,
    distinguishable and sintactically correct string. This method
    should not be used for runtime type identification, use enum
    {Sum}Functype and Item_func::functype()/Item_sum::sum_func()
    instead.
    Added here, to the parent class of both Item_func and Item_sum_func.

    NOTE: for Items inherited from Item_sum, func_name() return part of
    function name till first argument (including '(') to make difference in
    names for functions with 'distinct' clause and without 'distinct' and
    also to make printing of items inherited from Item_sum uniform.
  */
  virtual const char *func_name() const= 0;
};

class Item_ref :public Item_ident
{
protected:
  void set_properties();
public:
  enum Ref_Type { REF, DIRECT_REF, VIEW_REF, OUTER_REF, AGGREGATE_REF };
  Item **ref;
  Item_ref(Name_resolution_context *context_arg,
           const char *db_arg, const char *table_name_arg,
           const char *field_name_arg)
    :Item_ident(context_arg, db_arg, table_name_arg, field_name_arg),
     ref(0) {}
  /*
    This constructor is used in two scenarios:
    A) *item = NULL
      No initialization is performed, fix_fields() call will be necessary.
      
    B) *item points to an Item this Item_ref will refer to. This is 
      used for GROUP BY. fix_fields() will not be called in this case,
      so we call set_properties to make this item "fixed". set_properties
      performs a subset of action Item_ref::fix_fields does, and this subset
      is enough for Item_ref's used in GROUP BY.
    
    TODO we probably fix a superset of problems like in BUG#6658. Check this 
         with Bar, and if we have a more broader set of problems like this.
  */
  Item_ref(Name_resolution_context *context_arg, Item **item,
           const char *table_name_arg, const char *field_name_arg,
           bool alias_name_used_arg= FALSE);

  /* Constructor need to process subselect with temporary tables (see Item) */
  Item_ref(THD *thd, Item_ref *item)
    :Item_ident(thd, item), ref(item->ref) {}
  enum Type type() const		{ return REF_ITEM; }
  double val_real();
  longlong val_int();
  my_decimal *val_decimal(my_decimal *);
  bool val_bool();
  String *val_str(String* tmp);
  bool is_null();
  enum Item_result result_type () const { return (*ref)->result_type(); }
  enum_field_types field_type() const   { return (*ref)->field_type(); }
  Item *get_tmp_table_item(THD *thd);
  table_map used_tables() const		
  {
    return depended_from ? OUTER_REF_TABLE_BIT : (*ref)->used_tables(); 
  }

  table_map not_null_tables() const
  {
    /*
      It can happen that our 'depended_from' member is set but the
      'depended_from' member of the referenced item is not (example: if a
      field in a subquery belongs to an outer merged view), so we first test
      ours:
    */
    return depended_from ? OUTER_REF_TABLE_BIT : (*ref)->not_null_tables();
  }
  bool is_result_field() { return 1; }
  Item *real_item()
  {
    return ref ? (*ref)->real_item() : this;
  }
  bool walk(Item_processor processor, bool walk_subquery, uchar *arg)
  {
    return (*ref)->walk(processor, walk_subquery, arg) ||
           (this->*processor)(arg);
  }
  virtual bool explain_subquery_checker(uchar **arg)
  {
    /*
      Always return false: we don't need to go deeper into referenced
      expression tree since we have to mark aliased subqueries at
      their original places (select list, derived tables), not by
      references from other expression (order by etc).
    */
    return false;
  }
  virtual void print(String *str, enum_query_type query_type);
  Item_field *field_for_view_update()
    { return (*ref)->field_for_view_update(); }
  virtual Ref_Type ref_type() { return REF; }

  virtual bool basic_const_item() const { return ref && (*ref)->basic_const_item(); }

  /**
    Checks if the item tree that ref points to contains a subquery.
  */
  virtual bool has_subquery() const 
  { 
    DBUG_ASSERT(ref);
    return (*ref)->has_subquery();
  }

  /**
    Checks if the item tree that ref points to contains a stored program.
  */
  virtual bool has_stored_program() const 
  { 
    DBUG_ASSERT(ref);
    return (*ref)->has_stored_program();
  }

  virtual bool created_by_in2exists() const
  {
    return (*ref)->created_by_in2exists();
  }
};


#ifdef MYSQL_SERVER
#include "gstream.h"
#include "spatial.h"
#include "item_sum.h"
#include "item_func.h"
#include "item_row.h"
#include "item_cmpfunc.h"
#include "item_strfunc.h"
#include "item_geofunc.h"
#include "item_timefunc.h"
#include "item_subselect.h"
#include "item_xmlfunc.h"
#include "item_create.h"
#endif


class Cached_item :public Sql_alloc
{
public:
  my_bool null_value;
  Cached_item() :null_value(0) {}
  virtual bool cmp(void)=0;
  virtual ~Cached_item(); /*line -e1509 */
};

class Cached_item_str :public Cached_item
{
  Item *item;
  uint32 value_max_length;
  String value,tmp_value;
public:
  Cached_item_str(THD *thd, Item *arg);
  bool cmp(void);
  ~Cached_item_str();                           // Deallocate String:s
};


class Cached_item_real :public Cached_item
{
  Item *item;
  double value;
public:
  Cached_item_real(Item *item_par) :item(item_par),value(0.0) {}
  bool cmp(void);
};

class Cached_item_int :public Cached_item
{
  Item *item;
  longlong value;
public:
  Cached_item_int(Item *item_par) :item(item_par),value(0) {}
  bool cmp(void);
};

class Cached_item_temporal :public Cached_item
{
  Item *item;
  longlong value;
public:
  Cached_item_temporal(Item *item_par) :item(item_par), value(0) {}
  bool cmp(void);
};


class Cached_item_decimal :public Cached_item
{
  Item *item;
  my_decimal value;
public:
  Cached_item_decimal(Item *item_par);
  bool cmp(void);
};


class Item_default_value : public Item_field
{
public:
  Item *arg;
  Item_default_value(Name_resolution_context *context_arg)
    :Item_field(context_arg, (const char *)NULL, (const char *)NULL,
               (const char *)NULL),
     arg(NULL) {}
  Item_default_value(Name_resolution_context *context_arg, Item *a)
    :Item_field(context_arg, (const char *)NULL, (const char *)NULL,
                (const char *)NULL),
     arg(a) {}
  enum Type type() const { return DEFAULT_VALUE_ITEM; }
  virtual void print(String *str, enum_query_type query_type);
  table_map used_tables() const { return (table_map)0L; }

  bool walk(Item_processor processor, bool walk_subquery, uchar *args)
  {
    if (arg && arg->walk(processor, walk_subquery, args))
      return true;

    return (this->*processor)(args);
  }

};

/*
  Item_insert_value -- an implementation of VALUES() function.
  You can use the VALUES(col_name) function in the UPDATE clause
  to refer to column values from the INSERT portion of the INSERT
  ... UPDATE statement. In other words, VALUES(col_name) in the
  UPDATE clause refers to the value of col_name that would be
  inserted, had no duplicate-key conflict occurred.
  In all other places this function returns NULL.
*/

class Item_insert_value : public Item_field
{
public:
  Item *arg;
  Item_insert_value(Name_resolution_context *context_arg, Item *a)
    :Item_field(context_arg, (const char *)NULL, (const char *)NULL,
               (const char *)NULL),
     arg(a) {}
  virtual void print(String *str, enum_query_type query_type);

  /* 
   We use RAND_TABLE_BIT to prevent Item_insert_value from
   being treated as a constant and precalculated before execution
  */
  table_map used_tables() const { return RAND_TABLE_BIT; }

  bool walk(Item_processor processor, bool walk_subquery, uchar *args)
  {
    return arg->walk(processor, walk_subquery, args) ||
	    (this->*processor)(args);
  }
};


class Table_triggers_list;

/*
  Represents NEW/OLD version of field of row which is
  changed/read in trigger.

  Note: For this item main part of actual binding to Field object happens
        not during fix_fields() call (like for Item_field) but right after
        parsing of trigger definition, when table is opened, with special
        setup_field() call. On fix_fields() stage we simply choose one of
        two Field instances representing either OLD or NEW version of this
        field.
*/
class Item_trigger_field : public Item_field,
                           private Settable_routine_parameter
{
public:
  /* Is this item represents row from NEW or OLD row ? */
  enum row_version_type {OLD_ROW, NEW_ROW};
  row_version_type row_version;
  /* Next in list of all Item_trigger_field's in trigger */
  Item_trigger_field *next_trg_field;
  /*
    Next list of Item_trigger_field's in "sp_head::
    m_list_of_trig_fields_item_lists".
  */
  SQL_I_List<Item_trigger_field> *next_trig_field_list;
  /* Index of the field in the TABLE::field array */
  uint field_idx;
  /* Pointer to Table_trigger_list object for table of this trigger */
  Table_triggers_list *triggers;

  Item_trigger_field(Name_resolution_context *context_arg,
                     row_version_type row_ver_arg,
                     const char *field_name_arg,
                     ulong priv, const bool ro)
    :Item_field(context_arg,
               (const char *)NULL, (const char *)NULL, field_name_arg),
     row_version(row_ver_arg), next_trig_field_list(NULL), field_idx((uint)-1),
     original_privilege(priv), want_privilege(priv),
     read_only (ro)
  {}
  enum Type type() const { return TRIGGER_FIELD_ITEM; }
  virtual void print(String *str, enum_query_type query_type);
  table_map used_tables() const { return (table_map)0L; }

private:
  /*
    'want_privilege' holds privileges required to perform operation on
    this trigger field (SELECT_ACL if we are going to read it and
    UPDATE_ACL if we are going to update it).  It is initialized at
    parse time but can be updated later if this trigger field is used
    as OUT or INOUT parameter of stored routine (in this case
    set_required_privilege() is called to appropriately update
    want_privilege and cleanup() is responsible for restoring of
    original want_privilege once parameter's value is updated).
  */
  ulong original_privilege;
  ulong want_privilege;
  /*
    Trigger field is read-only unless it belongs to the NEW row in a
    BEFORE INSERT of BEFORE UPDATE trigger.
  */
  bool read_only;
};

class st_select_lex;

extern Item_result item_cmp_type(Item_result a,Item_result b);

extern const String my_null_string;

#endif /* ITEM_INCLUDED */