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Re: Function trunc() behaves in unexpected manner with different data types

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Merlin Moncure <mmoncure(at)gmail(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, "Nathan M(dot) Davalos" <n(dot)davalos(at)sharedmarketing(dot)com>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: Function trunc() behaves in unexpected manner with different data types
Date: 2011-02-25 15:21:25
Message-ID: 21330.1298647285@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-bugs
Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
> right -- in understand how floating point works -- but are you are
> saying that you are ok with the fact that (for example) a table with a
> floating point unique key could dump and not restore? more
> specifically, a binary dump would restore but a text dump would not.

pg_dump takes measures against that (see extra_float_digits).

> I think this is a problem with our implementation -- not all versions
> of 2183.68 as outputted from the server are the same internally.

It's an inherent property of float math.  Yes, we could set the default
value of extra_float_digits high enough that distinct internal values
always had distinct text representations, but trust me, you would not
like it.

			regards, tom lane

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Subject: Re: Function trunc() behaves in unexpected manner with different data types
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