The CHECK Constraint
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Enforces the domain integrity by restricting the values to be inserted in a column

Constraints are evaluated in the order in which they are defined

There is a possible to define multiple CHECK constraints on a single column

If check constraints defined at the table level it can be applied for the multiple columns


[CONSTRAINT constraint_name ] CHECK (expression)

where, constraint_name specifies the name of the constraint to be created.

expression specifies the conditions that define the check to be made on the column. It can be any expression arithmetic operation, relational operation or keywords :

  1. The IN keyword.
  2. The LIKE keyword.
  3. The BETWEEN keyword.

The rules regarding the creation of the CHECK constraint are as follows:

  • It can be created at the column level
  • It can be contain user-specified search condition
  • It cannot contain sub queries
  • It does not check the existing data in the table if created with the WITH NOCHECK option
  • It can reference other columns of the same table
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