From: Tom Lane <tgl@sss.pgh.pa.us>
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: robb@helical.com <robb@helical.com>
Cc: pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer
Date: Wed, 13 Mar 2024 10:12:10 -0400
Message-ID: <2043864.1710339130@sss.pgh.pa.us> (raw)
In-Reply-To: <CAKFQuwYyJT+HFcOqGA5nawKA4yOnMdbGdqRkKbBLZ5KWFzcg7Q@mail.gmail.com>
References: <18390-03499fe4f5a0ac71@postgresql.org>
<CAKFQuwYyJT+HFcOqGA5nawKA4yOnMdbGdqRkKbBLZ5KWFzcg7Q@mail.gmail.com>
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Tuesday, March 12, 2024, PG Bug reporting form <noreply@postgresql.org>
> wrote:
>> However, an nth-root calculation from that float result does NOT produce a
>> new float result:
> The issue is you expect dividing two integers to produce a float but that
> isn’t how that works. Dividing two integers produces an integer. In this
> case zero, or .1 rounded down/truncated.
Possibly adding to the OP's confusion: not one of these examples
contains any float arithmetic whatsoever. They're of type numeric.
=# select pg_typeof(2.5937424601000000^(1.0/10));
pg_typeof
-----------
numeric
(1 row)
See
https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-CONSTANTS-NUMERIC
which says
A numeric constant that contains neither a decimal point nor an
exponent is initially presumed to be type integer if its value
fits in type integer (32 bits); otherwise it is presumed to be
type bigint if its value fits in type bigint (64 bits); otherwise
it is taken to be type numeric. Constants that contain decimal
points and/or exponents are always initially presumed to be type
numeric.
A cast to float would occur only if the value is fed to an operator
that doesn't come in an exactly matching datatype.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, david.g.johnston@gmail.com, robb@helical.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer
In-Reply-To: <2043864.1710339130@sss.pgh.pa.us>
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