Trunc Function Not Specifying Decimals

I have the following in my table:

create table example (

     col_a int4,
     col_b int4,
     average_col = numeric


)

col_a = 309
col_b = 16

309 / 16 = 19.3125

When I do the following, I only get 19. Not (19.0, or 19.3125, 19.3):

TRUNC((col_a/col_b),1) = 19

What am I doing wrong?

>Solution :

Integers, floats, and numerics are stored differently and their math is different. This is a fundamental thing with computers, computers don’t do math like we do. Because you’re dividing integers, Postgres only does integer math. 309/16 is 19.

You need to cast at least one integer to a numeric (not a float, trunc with a second argument takes a numeric) then divide.

select trunc(309::numeric/16,1)

Demonstration