Обсуждение: ERROR: value out of range: underflow in numeric log calculation
Hi,
When executing log calculations (example below):
SELECT 1.0 * exp(-1.0 *(ln(2) * (1695993520/86400.0)) / 0.04) AS result_test;
The following error occurs.
ERROR: value out of range: underflow
I can find no way around this other than to wrap the calculation in a function with
exception when numeric_value_out_of_range then return 0;
However performance is impacted when performing calculations on multiple rows with a function call.
I can however understand that an individual might wish to know that the result of a calculation cannot be represented by the system due to its small value however I don’t believe it should be the default behaviour.
Thank you,
Neil Gallacher
Analyst/Programmer
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Gallacher Neil <Neil.Gallacher@gstt.nhs.uk> writes:
> When executing log calculations (example below):
> SELECT 1.0 * exp(-1.0 *(ln(2) * (1695993520/86400.0)) / 0.04) AS result_test;
> The following error occurs.
> ERROR: value out of range: underflow
Yup.
> I can however understand that an individual might wish to know that the result of a calculation cannot be represented
bythe system due to its small value however I don't believe it should be the default behaviour.
You'd be in a minority on that opinion. In this case you could work
around it by asking for the calculation to be done in numeric rather
than float8:
regression=# SELECT 1.0 * exp(-1.0 *(ln(2::numeric) * (1695993520/86400.0)) / 0.04) AS result_test;
result_test
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
(1 row)
but I'm not sure how far that covers your real use-case.
regards, tom lane