Re: Constant propagation and similar issues
От | Ross J. Reedstrom |
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Тема | Re: Constant propagation and similar issues |
Дата | |
Msg-id | 20000911104703.E13906@rice.edu обсуждение исходный текст |
Ответ на | Re: Constant propagation and similar issues (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Constant propagation and similar issues
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Список | pgsql-hackers |
On Mon, Sep 11, 2000 at 11:15:58AM -0400, Tom Lane wrote: > > Most of the datetime operations are not considered constant-foldable. > The reason is that type timestamp has a special value CURRENT that > is a symbolic representation of current time (this is NOT what now() > produces, but might be thought of as a data-driven way of invoking > now()). This value will get reduced to a simple constant when it is > fed into an arithmetic operation. Hence, premature evaluation changes > the results and would not be a correct optimization. > > AFAIK hardly anyone actually uses CURRENT, and I've been thinking of > proposing that we eliminate it to make the world safe for constant- > folding timestamp operations. (Thomas, any comments here?) > I checked the ansi SQL'99 docs, and CURRENT as a date special constant is not a part of the standard (although CURRENT is a keyword: it is used in the context of cursors) Ross -- Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu> NSBRI Research Scientist/Programmer Computer and Information Technology Institute Rice University, 6100 S. Main St., Houston, TX 77005
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