Question

What is DDL ? Write any two examples of DDL. ​

Answer 1

the full form of ddl is data definition language

Answer 2

DDL is Data Definition Language.

DDL Statements let you perform these tasks

1.CREATING A TABLE

use the CREATE TABLE statement to create

→Relational table which is basic structure to hold the user data.

—>Object table which is a table which uses object type for column definition.

To create relational table in your own schema you must have the CREATE TABLE system privilege.

to create a table in anothers schema you must have CREATE ANY TABLE system privilege

syntax :

CREATE TABLE tablename (column1 datatype(size) constraint[optional], column2 datatype(size) constraint[optional]);

constraint is optional depending upon the requirement we have to mention constraint type.

we can create a table from another table using 'AS'

create table employee AS select * from emp;

→in above statement it creates the table and it contains same values/columns and rows of emp table in employee table.

2.ALTERING THE TABLE

use the ALTER TABLE statement to alter the definition of a nonpartitioned table, a partitioned table, a table partition, or a table subpartition.

ALTER TABLE statement is used for

→add a new column

syntax: ALTER TABLE tablename

ADD column_name datatype(size);

—>modify an existing column

syntax: ALTER TABLE tablename

MODIFY column_name datatype(size);

here,

a.we can increase or decrease the width or precision of a numeric or character column.

b. we can change one data type to another data type.

—>drop a column

syntax: ALTER TABLE tablename

DROP column_name ;

a.with ALTER TABLE statement we can drop only one column at a time

b.once column is dropped ,it cannot be recovered.