what is Constraint? How many types of constraints in SQL ?

Answer Posted / m arunachalam

Constraints are used to limit the type of data that can go
into a table.

Constraints can be specified when a table is created (with
the CREATE TABLE statement) or after the table is created
(with the ALTER TABLE statement).

We will focus on the following constraints:

NOT NULL
UNIQUE
PRIMARY KEY
FOREIGN KEY
CHECK
DEFAULT

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