On Wed, Apr 02, 2008 at 05:49:37PM +0100, Ian Sillitoe wrote: > This is probably a stupid question that has a very quick answer, however it > would be great if someone could put me out of my misery... > > I'm trying to JOIN two tables (well a table and a resultset from a PL/pgsql > function) where a joining column can be NULL You can't, NULL is not a value like other values. > Unless I've missed something, the docs on > http://www.postgresql.org/docs/8.1/static/functions-comparison.html seem to > suggest that the concept is an example of bad programming and the workaround > (of switching on the 'transform_null_equals' config) is a hack. Is this all > true or did my logic just get screwed up at some point? Unless I've just > missed something obvious, it seems useful to be able to join two tables > based on a condition where they share a NULL column - is there another way > of doing this? 'transform_null_equals' won't help you at all here since it only help in the very specific case of comparing with a constant. The easiest is to think of NULL as meaning 'unknown'. Clearly you can't copare that usefully with anything. Perhaps you can use a marker like -1 to acheive the effect you want? Have a nice day, -- Martijn van Oosterhout <kleptog@xxxxxxxxx> http://svana.org/kleptog/ > Please line up in a tree and maintain the heap invariant while > boarding. Thank you for flying nlogn airlines.
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