Difference between revisions of "FOREIGN KEY Table Constraint"
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==Purpose== | ==Purpose== | ||
Table constraint to define a Foreign Key | Table constraint to define a Foreign Key | ||
| Line 34: | Line 27: | ||
==Example== | ==Example== | ||
<code lang="recital"> | <code lang="recital"> | ||
| − | + | ||
| − | CREATE TABLE supplier (SuppId i PRIMARY KEY, SuppName c(40) UNIQUE) | + | CREATE TABLE supplier; |
| − | CREATE TABLE purchase_order (POid i PRIMARY KEY, SuppId i, POtotal n(10,2) ) | + | (SuppId i PRIMARY KEY, SuppName c(40) UNIQUE) |
| − | ALTER TABLE purchase_order ADD FOREIGN KEY SuppID TAG SuppId REFERENCES supplier | + | CREATE TABLE purchase_order; |
| + | (POid i PRIMARY KEY, SuppId i, POtotal n(10,2)) | ||
| + | ALTER TABLE purchase_order; | ||
| + | ADD FOREIGN KEY SuppID TAG SuppId REFERENCES supplier | ||
</code> | </code> | ||
==Products== | ==Products== | ||
| − | Recital | + | Recital, Recital Server |
[[Category:Documentation]] | [[Category:Documentation]] | ||
[[Category:SQL]] | [[Category:SQL]] | ||
Latest revision as of 10:35, 22 December 2009
Purpose
Table constraint to define a Foreign Key
Syntax
FOREIGN KEY <expr> TAG <cTagName> [COLLATE <cCollateSequence>]
[REFERENCES <cTableName> [TAG <cTagName2>]]
See Also
ALTER TABLE, CONSTRAINTS, CREATE TABLE
Description
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. The <expr> can contain any valid index key. A tag index is built on the specified <expr>; it is given the name as defined in <cTagName>. A table may have more than one Foreign Key index.
The optional COLLATE <cCollateSequence> clause is included for Visual FoxPro language compatibility only.
The optional REFERENCES clause is used to create a relationship to an index key of another table. The value of the <expr> 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>. If the optional TAG <cTagName2> clause is omitted, the primary index key of <cTableName> is used. If <cTableName> has no index tags, an error is generated.
Example
CREATE TABLE supplier; (SuppId i PRIMARY KEY, SuppName c(40) UNIQUE) CREATE TABLE purchase_order; (POid i PRIMARY KEY, SuppId i, POtotal n(10,2)) ALTER TABLE purchase_order; ADD FOREIGN KEY SuppID TAG SuppId REFERENCES supplier
Products
Recital, Recital Server
