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List:       postgresql-general
Subject:    [GENERAL] Specify a column without using its name
From:       Andrew Biagioni <andrew.biagioni () e-greek ! net>
Date:       2003-11-30 23:39:25
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Hi all!

I'm trying to write a general-purpose trigger that determines what fields have 
changed during an UPDATE, but I'm running into a problem.

I'm trying to dynamically select the value from a field in "old" and "new" (the 
old and new values for the changed row), but I can't figure out how to do so.

I tried something like,

  qry := ''SELECT '' || fieldname || '' AS curval FROM old'';
  FOR rec IN EXECUTE qry LOOP
    fieldval := rec.curval;
    EXIT;
  END LOOP;

but it doesn't work ("ERROR:  OLD used in non-rule query").

Any suggestions?

Thanks,

		Andrew




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