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lab2_4-4.md

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+-- Create Table from existing table
+CREATE TABLE students_copy(idno, name, dob, cga, age) AS
+SELECT idno, name, dob, cgpa, age
+FROM students;
+
+-- User defined types
+/*  CREATE OR REPLACE TYPE <type_name>
+  AUTHID <CURRENT USER | DEFINER>
+  AS OBJECT (
+  <attribute> <attribute data_type>,
+  <inheritence clause>,
+  <subprogram spec>)
+  <FINAL | NOT FINAL> <INSTANTIABLE | NOT INSTANTIABLE>;
+  */
+
+CREATE OR REPLACE TYPE phone_t AS OBJECT (
+  a_code CHAR(3),
+  p_number CHAR(8));
+
+CREATE TABLE phone (
+  per_id NUMBER(10),
+  per_phone phone_t);
+
+INSERT INTO phone (per_id, per_phone)
+VALUES (1, phone_t('206', '555-1212'));
+
+SELECT p.per_phone.p_number
+FROM phone p
+WHERE p.per_phone.a_code = '206';
+
+SELECT * from phone;
+
+-- ALTER TABLE (BIG HEADER)
+/*  ALTER TABLE <table name> <action>; */
+
+--Rename table
+ALTER TABLE phone RENAME TO phone1;
+
+--Add [COLUMN]<column definition>
+/* Column definition may be types and constraints or any other ele of col def. */
+
+/*
+  RULES for adding a col :
+    1) add col anytime if NOT NULL isnt specified.
+    2) add NOT NULL in 3 steps
+      2.1) Add col without NOT NULL specified
+      2.2) Fill every row with data
+      2.3) Modify col to be NOT NULL
+*/
+alter table staff add email varchar(20);
+alter table students add hostel varchar(20);
+
+-- MODIFY <column name> [SET DEFAULT <value expression> | DROP DEFAULT]
+/* to change or drop specified default value. 
+  RULES for modifying a col :
+    1) can increase CHAR col's width anytime
+    2) can increase no of dig in NUMBER col anytime
+    3) can increase or decrease no of decimal places in NUMBER col anytime
+    if col is NULL for every row of table
+    4) can change its datatype
+    5) can decrease CHAR col's width
+    6) can decrease no of dig in NUMBER col
+*/
+alter table course modify compcode numeric(5,0);
+
+-- DROP COLUMN <column name>[CASCADE | RESTRICT]
+/* if ext dependencies, drop will be rejected. CASCADE will attempt to 
+    all external dependencies b4 deleting the col. RESTRICT is opp(default).
+*/
+alter table staff drop column email;
+
+-- ADD <tbale constraint>
+ALTER TABLE students ADD CONSTRAINT agecheck check(age>15);
+
+-- Add multiple things (constraints/cols)
+ALTER TABLE students ADD (
+  testcol number(9) NOT NULL,
+  constraint cgcheck check(cgpa>=2.0)
+);
+
+--DROP CONTRAINT <constraint name> {CASCADE | RESTRICT]
+alter table course drop constraint un_course;
+
+
+
+
+
+-- Generated Values (for auto generation of data use IDENTITY)
+/* following gives error , but is standard, not supported in oracle*/
+CREATE TABLE purchases (
+  orderno INTEGER GENERATED BY DEFAULT AS IDENTITY,
+  verndorid CHAR(5),
+  ordertime DATETIME
+);
+
+
+
+
+-- SEQUENCES (db obj that generates values)
+/* more general way of auto generating values */
+/*
+  CREATE SEQUENCE <sequence name> [AS <data type>]
+  [START WITH <signed numberic litreral>]
+  [INCREMENT BY <signed numberic literal>]
+  [MAXVALUE <signed numeric literal> | NO MAXVALUE]
+  [MINVALUE <signed numeric literal> | NO MINVALUE]
+  [CYCLE | NO CYCLE]
+*/
+
+CREATE SEQUENCE customers_seq
+  START WITH 1000
+  INCREMENT BY 1
+  NOCACHE
+  NOCYCLE;
+
+/* CACHE 30 - precomputing 30 seq values and keeping in memory. */
+SELECT customers_seq.NEXTVAL FROM DUAL;
+SELECT customers_seq.CURRVAL FROM DUAL;
+
+CREATE TABLE customers(
+  customer_id number(9) primary key, 
+  customer_name char(50)
+);
+
+INSERT INTO customers(customer_ID, customer_name) VALUES (customers_seq.nextval, 'Jiva');
+
+SELECT * from customers;
+
+
+
+-- Drop table <tablename> [CASCADE | RESTRICT];
+drop table students_copy;
+
+
+
+
+-- MODIFYING DATA (DML) 
+
+--1) INSERT
+  -- create new from old
+  create table customers_copy(
+    customer_id number(9) primary key,
+    customer_name char(50)
+  );
+
+  insert into customers_copy(customer_id, customer_name) select * from customers;
+
+--2) UPDATE
+  insert into students values ('2000A7PS001', 'lol', '04/Mar/1996', 9.2, 20, 'Mal', 1);
+
+  update students
+  set name='test', cgpa = '9.6'
+  where idno='2000A7PS001';
+
+  select * from students;
+
+
+--3) DELETE
+delete from students 
+where idno='2000A7PS001';
+
+cREATE TABLE LOL(
+NAME CHAR(20),
+id number(10));
+
+insert into LOL values ('lakhan', 7);
+select * from LOL;
+
+drop table LOL;
+/*
+TRUNCATE removes all rows without making entries into recovery 
+log but it can't be rolled back. TRUNCATE is faster than DELETE. 
+TRUNCATE is DDL statement and DELETE is a DML statement.
+*/
+
+
+-----------------EXERCISE--------------
+create table Category_details (
+  category_id numeric(2), 
+  category_name varchar(30)
+);
+
+create table Sub_category_details(
+  sub_category_id numeric(2),
+  category_id numeric(2),
+  sub_category_name varchar(30)
+);
+
+create table Product_details(
+  Product_id numeric (6),
+  category_id numeric(2),
+  sub_category_id numeric(2),
+  product_name varchar(30)
+);
+
+--1
+alter table category_details add constraint categorypk primary key(category_id);
+
+--2 (how to add without constraint name ? -> REMOVE KEYWORD CONSTRAINT)
+alter table sub_category_details add primary key(sub_category_id);
+
+--3
+alter table sub_category_details add constraint forkey foreign key(category_id) REFERENCING category_details(category_id);
+
+--4
+alter table product_details add(
+  constraint prodpk primary key(product_id), 
+  constraint forkeyprod foreign key(category_id) referencing category_details(category_id),
+  constraint subforkeyprod foreign key(sub_category_id) referencing sub_category_details(sub_category_id)
+);
+
+--5
+alter table product_details add price numeric(2);
+
+--6
+alter table product_details modify price numeric(6,2);
+
+--7
+
+
+
+
+
+
+
+
+