How to make postgresql SUM to be more accurate on large amount of floating point data?

I'm trying to SUM 8 million floating point (REAL) values with simple query like this:

SELECT SUM(metric) FROM metrics;

However, it returns very inaccurate result.
It should return 137,586.77, but it returns 137,303 (283.77 difference)

Is there a way to force a query to be more precise?

As per the postgresql documentation,


If you require exact storage and calculations (such as for monetary amounts), use the numeric type instead.

Since You've used real datatype, you can casting the real values to numeric. Then you can get results as you expected.

SELECT SUM(metric::NUMERIC) FROM metrics;

StackExchange Database Administrators Q#37658, answer score: 10