Lecture 3 sql {basics ddl commands}

LECTURE -3
S T R U C T U R E D Q U E R Y L A N G U A G E
D A T A D E F I N I T I O N L A N G U A G E ( D D L )
D e l i v e r e d B y :
M r . S h u b h a m S h u k l a

DATA DEFINITION LANGUAGE (DDL):
Three basic commands:
• CREATE
• DROP
• ALTER

CREATE
• CREATE TABLE Statement
Syntax
CREATE TABLE table_name
(
column1 datatype [ NULL | NOT NULL ],
column2 datatype [ NULL | NOT NULL ],
...
column_n datatype [ NULL | NOT NULL ]
);

Example:
CREATE TABLE customers
(
customer_id number(10) NOT NULL,
customer_name varchar2(50) NOT NULL,
city varchar2(50),
PRIMARY KEY (customer_id)
);

CREATE TABLE AS Statement:
Create Table - By Copying all columns from another table
Syntax
CREATE TABLE new_table
AS (SELECT * FROM old_table);
Create Table - By Copying selected columns from another table
Syntax
AS (SELECT column_1, column2, ... column_n FROM old_table);

Create table - By Copying selected columns from multiple tables:
Syntax
AS (SELECT column_1, column2, ... column_n
FROM old_table_1, old_table_2, ... old_table_n);
Example:
CREATE TABLE sup_cust
AS (SELECT customers.customer_id, customers.city, Supplier1.Supplier_name
FROM customers, Supplier1
WHERE customers.customer_id = Supplier1.Supplier_id);

ALTER
• ALTER TABLE Statement
Add Single column in table
Syntax
ALTER TABLE table_name
ADD column_name column-definition;
Example:
ALTER TABLE customers
ADD customer_name varchar2(45);

Add multiple columns in table
Syntax
ADD (column_1 column-definition,
column_2 column-definition,
...
column_n column_definition);
For example:
ADD (customer_name varchar2(45),
city varchar2(40));

Modify column in table
Syntax
MODIFY column_name column_type;
For example:
MODIFY customer_name varchar2(100) not null;

Modify Multiple columns in table
Syntax
MODIFY (column_1 column_type,
column_2 column_type,
...
column_n column_type);
For example:
MODIFY (customer_name varchar2(100) not null,
city varchar2(75));

Drop column in table
Syntax
DROP COLUMN column_name;
For example:
DROP COLUMN customer_name;

Rename column in table
Syntax
RENAME COLUMN old_name to new_name;
For example:
RENAME COLUMN customer_name to cname;

Rename table
Syntax
RENAME TO new_table_name;
For example:
RENAME TO contacts;

DROP
DROP TABLE Statement
Syntax
DROP TABLE [schema_name].table_name
[ CASCADE CONSTRAINTS ]
[ PURGE ];
CASCADE CONSTRAINTS: Optional. If specified, all referential integrity constraints will
be dropped as well.
PURGE: Optional. If specified, the table and its dependent objects will be purged from the
recycle bin and you will not be able to recover the table. If not specified, the table and its
dependent objects are placed in the recycle bin and can be recovered later, if needed.
For example:
DROP TABLE customers PURGE;

VIEW
• It is a virtual table that does not physically exist. Rather, it is created by a
query joining one or more tables.
Create VIEW
Syntax
CREATE VIEW view_name AS
SELECT columns
FROM tables
[WHERE conditions];

VIEW
Example:
CREATE VIEW sup_orders AS
SELECT suppliers.supplier_id, orders.quantity, orders.price
FROM suppliers
INNER JOIN orders
ON suppliers.supplier_id = orders.supplier_id
WHERE suppliers.supplier_name = 'Microsoft';

Update VIEW
Syntax
CREATE OR REPLACE VIEW view_name AS
SELECT columns
FROM table
WHERE conditions;

Example
CREATE or REPLACE VIEW sup_orders AS
SELECT suppliers.supplier_id, orders.quantity, orders.price
FROM suppliers
INNER JOIN orders
ON suppliers.supplier_id = orders.supplier_id
WHERE suppliers.supplier_name = 'Apple';

Drop VIEW
Syntax
DROP VIEW view_name;
Example
DROP VIEW sup_orders;

Lecture 3 sql {basics ddl commands}

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