Re: [HACKERS] indexes and floats

> > Ah-hah, all of a sudden this looks *real* familiar.  I bet it's
> > because pgsql is not noticing that "500.0" can be interpreted as a
> > float4. Let's try it.
>
> Oh, you have nailed it! This is interesting because (probably) a query
> like
>
>   select f4 from t4 where f4 = 500.0;
>
> is being automatically "upgraded" in the parser backend to
>
>   select f4 from t4 where float8(f4) = 500.0;
>
> So, since there is no functional index float8(f4) on the table we cannot
> use an existing index on f4 to advantage.
>
> This may be a result of my recent enhancements to the automatic type
> coersion code. But I'm a little suprised that v6.3.x doesn't just
> complain about a type mismatch but instead actually works. It may be
> that the old code which converted constants using intermediate strings
> worked (sort of) for this case. In general, the pre-enhancement code
> _only_ tried to convert constants, and complained about type mismatches
> when non-constants were involved.

Yes, it did numeric constants, I think.



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