Data Definition Language (DDL)
DDL Commands:
These Commands are used to define and modify the structure of a database and its objects, such as tables, indexes, views, and constraints.
Most popular Commands are:
- CREATE
- ALTER
- DROP
- TRUNCATE
CREATE Table:
This command is used to create a new table with specified columns and data types.
Syntax:
CREATE TABLE table_name (
column1 data_type,
column2 data_type,
— …
);
Example:
DROP Table:
This command is used to Deletes a table and its data from Existing Database.
Syntax:
DROP Table table_name;
Example:
DROP Table Employee;
TRUNCATE Table:
This command is used to delete the data inside a table but not table structure.
Syntax:
TRUNCATE Table table_name;
ALTER TABLE:
This command is used to add, delete, and modify columns in an existing table.
Syntax:
ALTER Table table_name
ADD column_name datatype;
Example:
ALTER Table Employee
ADD Email varchar(50);
ALTER TABLE – DROP Column:
To Drop a column Email from Employee Table use the following syntax:
ALTER Table Employee
DROP Column Email;
Alter Table – Rename Column:
To rename a column in a Table, use the following syntax:
ALTER Table table_name
RENAME Column old_name to new_name;
ALTER TABLE – Modify Datatype:
MYSQL:
ALTER TABLE table_name
MODIFY Column column-name datatype;
SQL Server:
ALTER TABLE table_name
ALTER Column column-name datatype;
