DESCRIPTION Column Constraint

Purpose

Column constraint to set the column description for the specified column

Syntax

DESCRIPTION <expC>

See Also

ALTER TABLE, CONSTRAINTS, CREATE TABLE, LABEL() METADATA_DECODE() COLUMNMETADATA()

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 DESCRIPTION column constraint is used to set the column description for the specified column. The <expC> is a character expression of up to 25 characters.

Note that the DESCRIPTION is store in the table structure (LIST STRUCTURE), not in the separate data dictionary file (LIST DICTIONARY).

For a Virtual Table, the DESCRIPTION constraint needs to be defined as the 'caption' in the column metadata, either in the MetaData Editor, or in code as below. It can be queried using the COLUMNMETADATA() function.

Example

ALTER TABLE customer;
  ADD COLUMN dateref DATE;
  DEFAULT date();
  DESCRIPTION "Date Reference"
 
// Virtual Table example
open database cloudlibtest
use vt_actors
alter table vt_actors modify constraint first_name metadata "caption=Forename"
? metadata_decode( columnmetadata("first_name") )