Difference between revisions of "PRIMARY KEY Table Constraint"

Revision as of 05:45, 8 December 2012

Purpose

Table constraint to define table's Primary Key

Syntax

PRIMARY KEY <expr> TAG <cTagName> [COLLATE <cCollateSequence>]

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 PRIMARY KEY table constraint is used to define <expr> as the table's Primary Key. The <expr> can contain any valid index key. A unique tag index is built on the specified <expr>; it is given the name as defined in <cTagName>. If a table already has a primary key defined, an error will be returned.

The optional COLLATE <cCollateSequence> clause is included for Visual FoxPro language compatibility only.

Example

CREATE TABLE newcust;
  (acc_ref char(5) default strzero(seqno(),5),;
  acc_name char(20))
 
ALTER TABLE newcust;
  ADD PRIMARY KEY acc_ref+acc_name TAG RefName

Products

Lianja, Lianja Server