Difference between revisions of "REFERENCES Column Constraint"

Revision as of 17:10, 8 December 2009

Purpose

Column constraint to create a relationship to an index key of another table

Syntax

REFERENCES <cTableName> [TAG <cTagName>]

See Also

ALTER TABLE, CONSTRAINTS, CREATE TABLE

Description

A constraint is used to define rules that help to provide data integrity. Column constraints are specific to the column name specified. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.

The REFERENCES column constraint is used to create a relationship to an index key of another table. The value of a column which has the REFERENCES column constraint set is validated by checking that it already exists as a value in the referenced index key.

The name of the referenced table is specified in <cTableName>. The index tag to reference is specified in <cTagName>. If the optional TAG <cTagName> clause is omitted, the primary index key of <cTableName> is used. If <cTableName> has no index tags, an error is generated.

Example

set sql to vfp
CREATE TABLE supplier ;
(SuppId i PRIMARY KEY, ;
SuppName c(40) UNIQUE)
CREATE TABLE purchase_order ;
(POid i PRIMARY KEY, ;
SuppId i REFERENCES supplier TAG SuppId, ;
POtotal n(10,2) )
list dictionary

Products

Recital, Recital Server