Re: AW: Re: [SQL] behavior of ' = NULL' vs. MySQL vs. Stand ards
От | Joe Conway |
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Тема | Re: AW: Re: [SQL] behavior of ' = NULL' vs. MySQL vs. Stand ards |
Дата | |
Msg-id | 00b101c0fc18$53ed01f0$0205a8c0@jecw2k1 обсуждение исходный текст |
Ответ на | AW: Re: [SQL] behavior of ' = NULL' vs. MySQL vs. Stand ards (Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>) |
Ответы |
Re: AW: Re: [SQL] behavior of ' = NULL' vs. MySQL vs. Stand ards
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Список | pgsql-hackers |
> For extra credit ;-) ... if you'd like to learn a little bit about the > optimizer, think about teaching clause_selectivity() in > optimizer/path/clausesel.c how to estimate the selectivity of these new > expression nodes. In the case where the argument is a boolean column > that we have statistics for, it should be possible to derive the correct > answer (including accounting for NULLs). If the argument is more > complex than that, you probably can't do anything really intelligent, > but you could handwave away NULLs and then compute the appropriate > function of the clause_selectivity() of the argument. Attached is my initial attempt to teach clause_selectivity about BooleanTest nodes, for review and comment. Please let me know if I'm headed in the right direction. Thanks, Joe
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