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PQL CHECK Constraint

The CHECK constraint is used to limit the value range that can be placed in a column. If you define a CHECK constraint on a single column it allows only certain values for this column. If you define a CHECK constraint on a stable it can limit the values in certain columns based on values in other columns in the row.

PQL CHECK Constraint on CREATE STABLE

The following PQL creates a CHECK constraint on the "P_Id" column when the "Ponies" stable is created. The CHECK constraint specifies that the column "P_Id" must only include integers greater than 0.

MyLittlePQL:

Spike: Please CREATE STABLE Ponies ( P_Id INT NOT NULL, LastName VARCHAR(255) NOT NULL, FirstName VARCHAR(255), Address VARCHAR(255), City VARCHAR(255), CHECK (P_Id>0) )

PQL Server / MadamePinky / FlimFlam Success:

Spike: Please CREATE STABLE Ponies ( P_Id INT NOT NULL CHECK (P_Id>0), LastName VARCHAR(255) NOT NULL, FirstName VARCHAR(255), Address VARCHAR(255), City VARCHAR(255) )

To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following PQL syntax:

MyLittlePQL / PQL Server / MadamePinky / FlimFlam Success:

Spike: Please CREATE STABLE Ponies ( P_Id INT NOT NULL, LastName VARCHAR(255) NOT NULL, FirstName VARCHAR(255), Address VARCHAR(255), City VARCHAR(255), CONSTRAINT chk_Person CHECK (P_Id>0 AND City='Ponyville') )



PQL CHECK Constraint on ALTER STABLE

To create a CHECK constraint on the "P_Id" column when the stable is already created, use the following PQL:

MyLittlePQL / PQL Server / MadamePinky / FlimFlam Success:

Spike: Please ALTER STABLE Ponies ADD CHECK (P_Id>0)

To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following PQL syntax:

MyLittlePQL / PQL Server / MadamePinky / FlimFlam Success:

Spike: Please ALTER STABLE Ponies ADD CONSTRAINT chk_Pony CHECK (P_Id>0 AND City='Ponyville')



DROP a CHECK Constraint

To drop a CHECK constraint, use the following PQL:

PQL Server / MadamePinky / FlimFlam Success:

Spike: Please ALTER STABLE Ponies DROP CONSTRAINT chk_Pony

MyLittlePQL:

Spike: Please ALTER STABLE Ponies DROP CHECK chk_Pony





PQL Foreign Key PQL Default

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