maintaining a field for every UPDATION.

Hello all,

My need is something like this..

Consider in my database i have around 200 tables. In all my tables i
would like to maintain below 2 mandatory fields.

create_time timestamp,
modify_time timestamp.

So, for every insertions i would like to maintain create_time and i
had it, by setting default value to now() to that column.

Well, now i would like to maintain modify_time for every updation. how
can i? Using common plpgsql function i cant even able to refer OID
even during UPDATION. The result is

ERROR:  record old has no field oid    or
ERROR:  record new has no field oid

One way: i can have seperate plpgsql function for every table and
apply conditions accordingly. But i dont think thats the consistent
way.

how else can i maintain modify_time field ?

Thankx in advance.

======================================================================Of course you have a purpose -- to find a
purpose.
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Regards,
Bhuvaneswar.