Re: Where can I find detail information about constraint ?

??? wrote:
> I want detail usage introduction about constraint,such as how 
> to constrain a string to be exactly 4 character and start with 'z'.
> Where can I find the reference of CHECK? detail usage.

Documentation:
http://www.postgresql.org/docs/current/static/ddl-constraints.html#AEN2254

The check you want would look similar to this:
CHECK (length(val) = 4 AND substr(val, 1, 1) = 'z')

Yours,
Laurenz Albe