Jack Christensen <j...@jackchristensen.com> writes:
> jack=# select '1.51 years'::interval = '1.52 years'::interval;
>   ?column?
> ----------
>   t
> (1 row)

> This is surprising. Once I looked at the C code for Interval it makes 
> more sense given that it cannot represent fractional years, months, or 
> days. Wouldn't it make more sense to raise an invalid input error than 
> to silently truncate data?

Well, "1.5 years" is perfectly valid (it means 18 months).  So I don't
think rejecting fractional years altogether would be a good idea.

Really your complaint is not very different from complaining because
1.23456789::float4 = 1.234567891::float4.  It's just a property of the
datatype that certain inputs aren't represented exactly.  Another example
that stays within the interval datatype is

regression=# select '1.000001 seconds'::interval;
    interval     
-----------------
 00:00:01.000001
(1 row)

regression=# select '1.0000001 seconds'::interval;
 interval 
----------
 00:00:01
(1 row)

I doubt people would thank us for rejecting that second input altogether.

                        regards, tom lane


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