Cast syntax to convert a sum to float

问题

Using PostgreSQL 9.3, I want to convert the calculated values to data type float.

My first attempt:

SELECT float(SUM(Seconds))/-1323 AS Averag;

Gives me this error:

syntax error at or near "SUM"

My second attempt:

SELECT to_float(SUM(Seconds))/-1323 AS Averag;

Gives me this error:

 function to_float(bigint) does not exist

回答1:

You need to use the cast syntax:

SELECT CAST (SUM(Seconds) AS FLOAT)/-1323 AS Averag;

回答2:

There is also the shorthand cast syntax:

SELECT sum(seconds)::float / -1323 AS averag;

• Postgres data type cast

回答3:

It is not exact casting but a trick to do the job :) and works almost in any language.

SELECT SUM(Seconds)/-1323.0 AS Averag;

OR

SELECT SUM(Seconds)*1.0/-1323 AS Averag;

来源：https://stackoverflow.com/questions/28736227/cast-syntax-to-convert-a-sum-to-float