domain feature - details

Hi all:
More details on what domains are. Domains are global
column definitions, upon which column definitions
can be based. A domain specifies a data type, and a
set of column attributes and constraints. Subsequent
table definitions can use the domain to define columns.

Here is the detail for 'ALTER DOMAIN' feature. I
pulled this off the chapter 42 at
http://sunsite.unc.edu/LDP/HOWTO/Database-HOWTO.html

<alter domain statement> ::=
         ALTER DOMAIN <domain name> <alter domain action>

     <alter domain action> ::=
           <set domain default clause>
         | <drop domain default clause>
         | <add domain constraint definition>
         | <drop domain constraint definition>

     <set domain default clause> ::= SET <default clause>

     <drop domain default clause> ::= DROP DEFAULT

     <add domain constraint definition> ::=
         ADD <domain constraint>

     <drop domain constraint definition> ::=
         DROP CONSTRAINT <constraint name>

     <drop domain statement> ::=
         DROP DOMAIN <domain name> <drop behavior>

And the create domain syntax is as follows:---
<domain definition> ::=
         CREATE DOMAIN <domain name>
             [ AS ] <data type>
           [ <default clause> ]
           [ <domain constraint>... ]
           [ <collate clause> ]

     <domain constraint> ::=
         [ <constraint name definition> ]
         <check constraint definition> [ <constraint attributes> ]

(To search a word in chapter 42, use CTRL+F in browser)
I hope to see this in postgreSQL 6.4

al
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