On Jan 17, 4:20 am, Naga lenoj <nagale... (AT) gmail (DOT) com> wrote:
PostgreSQL was designed explicitly to handle this kind of problem.

Have a look at the entire manual section here:

http://www.postgresql.org/docs/8.1/static/extend.html

with particular attention to:

http://www.postgresql.org/docs/8.1/static/xtypes.html

and the few sections following.

What you want to do here is to define a new relational 'domain' (note:
NOT a SQL DOMAIN, which is simply a renaming of another base type).
Validity checking is done (mostly) when queries are parsed.

I am also going to guess that your new 'data type/DOMAIN' has other
requirements, such as ordering. Does "AA123" come before or after
"12345", for example?

You can define your new data type / domain and any rules that you wish
to apply over it in 'C', PL or Tcl.