Is it possible to place a trigger on a field instead of entire row

[SkyHigh]

Hi

The subject says it all, or is there any other way to implement this functionality in postgres, has anyone done it

Thanks for your help
Brenda

 

[SkyHigh]

Let me explain a little bit to what I am trying to do here, I have a table with 12 columns and I want to archive a record before update when the value of a particular field in a record changes.

Any help would be appreciated.
Regards
Brenda

 

[rycamor]

Well, the answer is no and yes. Meaning: triggers are run on tables, not rows or fields, but that is really not a problem. You can't have a change on any particular column of a row, without it affecting the table. So, just write a function that checks for the old value of the column for any row, and if the value changes, then perform your archiving for that row. Now, set a BEFORE UPDATE (or BEFORE DELETE OR UPDATE) trigger on that table to call this function. Thus, whenever any row is updated, your function will check for a new value in that column, and if there is a new value, it will perform your backup.

See:

http://www.postgresql.org/idocs/index.php?sql-createtrigger.html

http://www.ca.postgresql.org/docs/aw_pgsql_book/node162.html

http://www.postgresql.org/idocs/index.php?programmer-pl.html

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[SkyHigh]

Thanks Rycamor, its really appreciated, I will try to write one, if stuck, then I will post it, see if you can help then.

The stuff you sent is indeed very helpful.
Thanks once again
Brenda