The following bug has been logged online:

Bug reference: 2356
Logged by: Philip Crotwell
Email address: crotwell (AT) seis (DOT) sc.edu
PostgreSQL version: 8.1
Operating system: linux
Description: sqrt and cbrt return different types
Details:

The return of sqrt() is numeric but the return type of cbrt is double, which
is confusing. So, for example this works:
select mod(sqrt(4.1), 4);
but this
select mod(cbrt(4.1), 4);
fails with
ERROR: function mod(double precision, integer) does not exist
and you have to do this instead:
select mod(CAST (cbrt(4.1) AS NUMERIC), 4);

It seems to me that square root and cube root should be the same in return
type.

The docs should be updated if this change is made:
http://www.postgresql.org/docs/8.1/i...ions-math.html

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"Philip Crotwell" <crotwell (AT) seis (DOT) sc.edu> writes:
They are, or at least one form of them matches:

regression=# \df sqrt
List of functions
Schema | Name | Result data type | Argument data types
------------+------+------------------+---------------------
pg_catalog | sqrt | double precision | double precision
pg_catalog | sqrt | numeric | numeric
(2 rows)

regression=# \df cbrt
List of functions
Schema | Name | Result data type | Argument data types
------------+------+------------------+---------------------
pg_catalog | cbrt | double precision | double precision
(1 row)


I think your request really amounts to "we should require every numeric
function to have a float8 counterpart and vice versa". Life's a bit too
short for that, though.

regards, tom lane

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