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* BUG #18390: exponentiation produces float datatype, but nth-root produces integer
@ 2024-03-13 02:57 PG Bug reporting form <noreply@postgresql.org>
2024-03-13 12:07 ` Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer David G. Johnston <david.g.johnston@gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: PG Bug reporting form @ 2024-03-13 02:57 UTC (permalink / raw)
To: pgsql-bugs@lists.postgresql.org; +Cc: robb@helical.com
The following bug has been logged on the website:
Bug reference: 18390
Logged by: Robb Allan
Email address: robb@helical.com
PostgreSQL version: 15.5
Operating system: Mac OS Sonoma 14.3.1 (23D60)
Description:
An exponentiation from a float produces a floating point result:
funds=# select (1.1^10);
?column?
--------------------
2.5937424601000000
(1 row)
However, an nth-root calculation from that float result does NOT produce a
new float result:
funds=# select (2.5937424601000000^(1/10));
?column?
--------------------
1.0000000000000000
(1 row)
Only when the root factors are floats does the result coerce to a float:
funds=# select (2.5937424601000000^(1.0/10));
?column?
------------------------
1.10000000000000000000
(1 row)
funds=# select (2.5937424601000000^(1/10.0));
?column?
------------------------
1.10000000000000000000
(1 row)
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer
2024-03-13 02:57 BUG #18390: exponentiation produces float datatype, but nth-root produces integer PG Bug reporting form <noreply@postgresql.org>
@ 2024-03-13 12:07 ` David G. Johnston <david.g.johnston@gmail.com>
2024-03-13 14:12 ` Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 3+ messages in thread
From: David G. Johnston @ 2024-03-13 12:07 UTC (permalink / raw)
To: robb@helical.com <robb@helical.com>; pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
On Tuesday, March 12, 2024, PG Bug reporting form <noreply@postgresql.org>
wrote:
> The following bug has been logged on the website:
>
> Bug reference: 18390
> Logged by: Robb Allan
> Email address: robb@helical.com
> PostgreSQL version: 15.5
> Operating system: Mac OS Sonoma 14.3.1 (23D60)
> Description:
>
> However, an nth-root calculation from that float result does NOT produce a
> new float result:
>
> funds=# select (2.5937424601000000^(1/10));
> ?column?
> --------------------
> 1.0000000000000000
> (1 row)
>
>
1.000000000000…. Is a float.
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.
David J.
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer
2024-03-13 02:57 BUG #18390: exponentiation produces float datatype, but nth-root produces integer PG Bug reporting form <noreply@postgresql.org>
2024-03-13 12:07 ` Re: BUG #18390: exponentiation produces float datatype, but nth-root produces integer David G. Johnston <david.g.johnston@gmail.com>
@ 2024-03-13 14:12 ` Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 0 replies; 3+ messages in thread
From: Tom Lane @ 2024-03-13 14:12 UTC (permalink / raw)
To: David G. Johnston <david.g.johnston@gmail.com>; +Cc: robb@helical.com <robb@helical.com>; pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
"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
^ permalink raw reply [nested|flat] 3+ messages in thread
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2024-03-13 02:57 BUG #18390: exponentiation produces float datatype, but nth-root produces integer PG Bug reporting form <noreply@postgresql.org>
2024-03-13 12:07 ` David G. Johnston <david.g.johnston@gmail.com>
2024-03-13 14:12 ` Tom Lane <tgl@sss.pgh.pa.us>
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