FOREIGN KEY Table Constraint
Table constraint to define a Foreign Key
FOREIGN KEY <column> | (<column>) [TAG <cTagName>] [REFERENCES <cTableName> TAG <cTagName2>]
A constraint is used to define rules that help to provide data integrity. TABLE constraints apply to table-based operations. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.
The FOREIGN KEY table constraint is used to define <expr> as a Foreign Key for a parent table. A tag index is built on the specified <column>; it is given the name as defined in <cTagName>. If <cTagName> is not specified, the tag index is given the same name as the <column>. A table may have more than one Foreign Key index.
The REFERENCES clause is used to create a relationship from the column, <column>, to an index key of another table. The value of the <column> 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 <cTagName2>.
The optional COLLATE <cCollateSequence> clause is included for Visual FoxPro language compatibility only.
CREATE TABLE supplier; (SuppId int PRIMARY KEY,; SuppRef char(10) UNIQUE,; SuppName char(40) UNIQUE) CREATE TABLE purchase_order; (POId int PRIMARY KEY,; PO_SuppRef char(10),; POtotal num(10,2)) ALTER TABLE purchase_order ADD FOREIGN KEY po_suppref TAG fk_po_suppref ALTER TABLE purchase_order ADD FOREIGN KEY (po_suppref) TAG fk_po_suppref; REFERENCES supplier TAG SuppRef
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