Hi there,

I'm trying to implement a "versionned" storage for a datawarehouse
system, meaning I have tables which store daily information about
objects and I would like to have a row inserted (i.e. a new version)
only if it differs from the most recent existing row. For instance
instead of storing

version attribute1 attribute2
1 x y
2 x y
3 x y
4 z y
5 z y
6 z t

we would only keep the diffs :

version attribute1 attribute2
1 x y
4 z y
6 z t

This would save lots of space and the full table could be easily
accessed through a view.

However as the tables have a large number of rows (several hundreds) I
would like to avoid having to write conditions like WHERE (old.att1 !=
new.attr1 or old.attr2 != new.attr2 or ... or old.attr245 != new.attr245
)

So my question is: is there a way to do some kind of whole-row
comparison ? For instance a hash of the full row or something similar ?
Is there a standard way of solving this problem ?

Thanks a lot for any hind !
Christian

> So my question is: is there a way to do some kind of whole-row
> comparison ? For instance a hash of the full row or something similar ?
> Is there a standard way of solving this problem ?

Sure it is called row wise comparison:
http://www.postgresql.org/docs/8.2/i...ISE-COMPARISON

you can write something like:

SELECT *
FROM Your_table
WHERE (c1,c2,c3,c4) = ('a',2,'xyz',123);

Regards,
Richard Broersma Jr.

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