BUG#22202665 - ADDING A TRIGGER TO A TABLE CHANGES THE BEHAVIOUR OF N…

…ULL DETECTION

For non-strict mode attempt to implicitly insert NULL value into NOT NULL
column led to a different results depending on whether trigger is set
or not. Implicit insert means here the following use case:
  CREATE TABLE t1 (a INT, b INT NOT NULL);
  SET sql_mode= '';
  INSERT INTO t1 (a) VALUES (1);
For such use case for mysql server before 5.7 the warning 1364
"Field 'b' doesn't have a default value" was issued.
In 5.7 the error 1048  "Column 'b' cannot be null" is issued.
Such behaviour broke backward compatibility with 5.6.

The reason for different behaviour in error handling of implicit NOT NULL
constraint violation was that prior 5.7 checking for presense of all
non-default values in INSERT statement was done before filling record
by column values. So any attempt to INSERT a record without specifying all
columns that doesn't have default values led to warning 1364. As of 5.7
checking for presence of non-default values is done after record is filled and
NOT NULL constraints has been already checked for ever table's field.
This leads to the fact that error 1048 is issued instead of warning 1364.

To fix the bug that broke backward compatibility checking for NOT NULL
violation is done only for fields set during handling INSERT statement.
In other words, for only those fields that is set in
field->table->fields_set_during_insert checking for NOT NULL is done.

mysql-test/r/trigger_wl6030.result

@@ -875,12 +875,10 @@ END|
 
 INSERT INTO t1(a) VALUES (1), (2), (3), (4), (5), (6);
 Warnings:
-Warning	1048	Column 'b' cannot be null
 Warning	1364	Field 'b' doesn't have a default value
 
 REPLACE INTO t1(a) VALUES (1), (2), (3), (4), (5), (6);
 Warnings:
-Warning	1048	Column 'b' cannot be null
 Warning	1364	Field 'b' doesn't have a default value
 
 SELECT * FROM t1;
@@ -2221,3 +2219,21 @@ SET sql_mode = @sql_mode_saved;
 Warnings:
 Warning	3090	Changing sql mode 'NO_AUTO_CREATE_USER' is deprecated. It will be removed in a future release.
 DROP TABLE t1;
+SET @sql_mode_saved = @@sql_mode;
+SET sql_mode='';
+CREATE TABLE t1(a INT NOT NULL, b INT NOT NULL);
+INSERT INTO t1(a) VALUES (1);
+Warnings:
+Warning	1364	Field 'b' doesn't have a default value
+SHOW WARNINGS;
+Level	Code	Message
+Warning	1364	Field 'b' doesn't have a default value
+CREATE TRIGGER t1_trg_before_ins BEFORE INSERT ON t1 FOR EACH ROW SET NEW.a=2;
+INSERT INTO t1(a) VALUES (1);
+Warnings:
+Warning	1364	Field 'b' doesn't have a default value
+SHOW WARNINGS;
+Level	Code	Message
+Warning	1364	Field 'b' doesn't have a default value
+SET sql_mode = @sql_mode_saved;
+DROP TABLE t1;

mysql-test/t/trigger_wl6030.test

@@ -1814,3 +1814,22 @@ SHOW WARNINGS;
 SET sql_mode = @sql_mode_saved;
 DROP TABLE t1;
 
+#
+# BUG#22202665 - ADDING A TRIGGER TO A TABLE CHANGES THE BEHAVIOUR OF NULL DETECTION
+#
+
+--disable_warnings
+SET @sql_mode_saved = @@sql_mode;
+SET sql_mode='';
+--enable_warnings
+CREATE TABLE t1(a INT NOT NULL, b INT NOT NULL);
+INSERT INTO t1(a) VALUES (1);
+SHOW WARNINGS;
+CREATE TRIGGER t1_trg_before_ins BEFORE INSERT ON t1 FOR EACH ROW SET NEW.a=2;
+INSERT INTO t1(a) VALUES (1);
+SHOW WARNINGS;
+
+--disable_warnings
+SET sql_mode = @sql_mode_saved;
+--enable_warnings
+DROP TABLE t1;

sql/sql_base.cc

@@ -9245,6 +9245,32 @@ bool check_record(THD *thd, Field **ptr)
 }
 
 
+/**
+  Check the NOT NULL constraint on all the fields explicitly set
+  in INSERT INTO statement or implicitly set in BEFORE trigger.
+
+  @param thd  Thread context.
+  @param ptr  Fields.
+
+  @return Error status.
+*/
+
+static bool check_inserting_record(THD *thd, Field **ptr)
+{
+  Field *field;
+
+  while ((field = *ptr++) && !thd->is_error())
+  {
+    if (bitmap_is_set(field->table->fields_set_during_insert,
+                      field->field_index) &&
+        field->check_constraints(ER_BAD_NULL_ERROR) != TYPE_OK)
+      return true;
+  }
+
+  return thd->is_error();
+}
+
+
 /**
   Check if SQL-statement is INSERT/INSERT SELECT/REPLACE/REPLACE SELECT
   and trigger event is ON INSERT. When this condition is true that means
@@ -9380,7 +9406,7 @@ fill_record_n_invoke_before_triggers(THD *thd, List<Item> &fields,
 
     table->triggers->disable_fields_temporary_nullability();
 
-    return rc || check_record(thd, table->field);
+    return rc || check_inserting_record(thd, table->field);
   }
   else
   {
@@ -9535,7 +9561,7 @@ fill_record_n_invoke_before_triggers(THD *thd, Field **ptr,
   if (rc)
     return true;
 
-  return check_record(thd, ptr);
+  return check_inserting_record(thd, ptr);
 }
 
 

sql/sql_insert.cc

@@ -1945,6 +1945,7 @@ int check_that_all_fields_are_given_values(THD *thd, TABLE *entry,
       err= 1;
     }
   }
+  bitmap_clear_all(write_set);
   return (!thd->lex->is_ignore() && thd->is_strict_mode()) ? err : 0;
 }