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Archives of the TeradataForum
Message Posted: Wed, 01 Dec 2004 @ 18:17:36 GMT
| Subj: | | Re: ("1=1") condition in the explain plan |
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| From: | | Victor Sokovin |
| | Sometimes in the explain plan of some SQL we see ("1=1") condition when it is doing the product join. We do not see this condition in all
product joins. | |
| | I will appreciate if somebody explains me in what circumstances optimizer uses ("1=1") condition? | |
| | Having this condition in the explain is bad? | |
I don't know when exactly the optimizer puts the ("1=1") condition in the plan (that's probably the idiosyncrasies of the code) but I
believe it makes no difference to the product join. It is always the same product join. To have it in the explain is not necessarily a bad thing
as it is one of the normal tools the optimizer may use. The only thing you should check is that the smaller tables get redistributed. Usually it
is (much) better. In some rare cases, though, the redistribution of the larger tables cannot be avoided, and it can still be the best strategy.
Anyway, product joins on the explain plan are not a reason for any panic.
Regards,
Victor
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