SQL constraints are used to specify rules for the data in a table

By DIBYAJYOTI PANDA

DESCRIPTION

SQL constraints are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted.

Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table. The following constraints are commonly used in SQL :

NOT NULL

Ensures that a column cannot have a NULL value

UNIQUE

Ensures that all values in a column are different

PRIMARY KEY

A combination of a NOT NULL and UNIQUE. Uniquely identifies each row in a table

FOREIGN KEY

Uniquely identifies a row/record in another table

CHECK

Ensures that all values in a column satisfies a specific condition

DEFAULT

Sets a default value for a column when no value is specified

INDEX

Used to create and retrieve data from the database very quickly

Spread the words

Share on facebook
Share on google
Share on twitter
Share on linkedin