Accessing fields in RECORD data type using variables as field names

Hi,

I am trying to write a generic audit-trail trigger function which will
record changes on a field-by-field basis to a single table for all audited
tables.

However, I find that I can only access a field in OLD and NEW if I know the
name in advance. Is there any way I can access the fields when I only have
a variable containing the name of the field?

If I can do this, I can make a really simple, schema-change-resistent, low
storage size audit trail for high read / low change databases.

Alistair

this is what I want to do:

FOR mcolumn IN EXECUTE ''SELECT col FROM v_cols_tables WHERE tbl = '' ||
quote_literal(TG_RELNAME) LOOP
vold = OLD.mcolumn.col; <--THIS BREAKS
vnew = NEW.mcolumn.col; <--THIS TOO!`
IF vold <> vnew THEN
--do audit trail stuff in here...
END IF;
END LOOP;