Friday, 15 February 2013

What are the SQL Constraints

SQL Constraints
Constraints are the rules enforced on a Table Colulmns 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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