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>
I am running PostgreSQL 9.4.4 on Fedora 22. >
> SELECT floor(4.725 * 100 + 0.5) returns 473, which is what I
expected.
>
> SELECT floor(4.725 * power(10, 2) + 0.5) returns 472, which I find
surprising.
>
> Please can someone explain the anomaly.
I think I have a solution to my problem, but I would appreciate a review in
case I have missed some corner cases.
I understand it better now. Here are some of the things I have
learned.
1. In Python, 4.725 is assumed to be a float. You need some extra steps to
turn it into a Decimal type. PostgreSQL seems to take the opposite approach – it
is assumed to be numeric, unless you explicitly cast it to a float.
2. As pointed out, there are two forms of the power function.
test=> select pg_typeof(power(10, 2));
pg_typeof
------------------
double precision
test=> select pg_typeof(power(10., 2));
pg_typeof
----------
numeric
I found that adding a decimal point after the 10 is the easiest way to
force it to return a numeric.
Putting this together, my solution is -
test=> select floor(4.725 * power(10., 2) + 0.5);
floor
-------
473
Can anyone see any problems with this?
Thanks
Frank
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