Re: Constant propagation and similar issues

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(at)rice(dot)edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005