Re: casts and conversions

This thread is not worth adding to TODO.detail, is it?


> "Josh Berkus" <josh@agliodbs.com> writes:
> > And, just to throw a banana peel onto the sidewalk of argument, there is
> > even a reason to keep things the way they are.  [ ... ]
> > Thus there's a good reason for the database to be indecisive about
> > float/numeric decisions, and good reason for you to explicitly CAST.
> 
> Indeed.  However, the SQL92 spec has its mind made up: section 6.12 says
> 
>          1) If the data type of both operands of a dyadic arithmetic opera-
>             tor is exact numeric, then the data type of the result is exact
>             numeric, [ ... ]
> 
>          2) If the data type of either operand of a dyadic arithmetic op-
>             erator is approximate numeric, then the data type of the re-
>             sult is approximate numeric.
> 
> So it's clear that for spec conformance we should cast numeric to float8
> and do the multiply in float math.  (Never mind that this could result
> in loss of precision or even overflow :-( since PG's numerics actually
> have a wider range of values than float8.)
> 
> A closely related issue is that SQL92 expects a literal like "1.234"
> to be considered exact numeric, not approximate, so our initial typing
> of such literals as float8 is wrong too.  We'll have to fix literal
> processing as well as the float8-vs-numeric-preference issue before we'll
> have spec-compliant processing of expressions like "numericvar * 1.234".
> (And yes, there's been lots and lots of discussion about how to do that,
> too...)
> 
>             regards, tom lane
> 
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