Thank you for your answer. I guess I better
create this history in the application's data class.
Klint Gore wrote:
Fernando
wrote:
I want to keep a history of changes on a
field in a table. This will be the case in multiple tables.
Can I create a trigger that loops the OLD and NEW values and compares
the values and if they are different creates a change string as
follows:
e.g;
FOR EACH field IN NEW
IF field.value <> OLD.field.name THEN
changes := changes
|| field.name
|| ' was: '
|| OLD.field.value
|| ' now is: '
|| field.value
|| '\n\r';
END IF
END FOR;
Your help is really appreciated.
You can't in plpgsql. It doesn't have the equivalent of a walkable
fields collection. Its possible in some other procedure languages
(I've seen it done in C).
Having said that, you might be able to create new and old temp tables
and then use the system tables to walk the columns list executing sql
to check for differences.
something like
create temp table oldblah as select old.*;
create temp table newblah as select new.*;
for arecord in
select columnname
from pg_??columns??
join pg_??tables?? on ??columns??.xxx = ??tables??.yyy
where tablename = oldblah and pg_table_is_visible
loop
execute 'select old.' || arecord.columname || '::text , new. '
|| arecord.columname || '::text' ||
' from oldblah old, newblah new ' ||
' where oldblah.' || arecord.columnname || '
<> newblah.' ||arecord.columnname into oldval,newval;
changes := changes || arecord.columnname || ' was ' || oldval ||
' now ' || newval;
end loop;
execute 'drop table oldblah';
execute 'drop table newblah';
performance could be awful though.
klint.
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