为什么我的float在postgreSQL中显示为0

Question

One of my columns process_size holds a value 800089856 in bytes .

My SQL query says

select ((process_size*11/(1024*1024*1024))*100)/(4*3600) as Avg_wk_sum from instances where wk_id = 2

But instead of a float value it shows 0 .

I even tried explicit cast

select ((process_size*11/(1024*1024*1024))*100)/(4*3600) :: float as Avg_wk_sum from instances where wk_id = 2

What am I doing wrong? How can I get the float value?

Answer 1

All values in your statement are integers, so the actual division/multiplication is carried out using integers - which yields 0. You then cast the result ( 0 ) to a float which doesn't change anything.

You should cast process_size to a float, then all subsequent operations are carried out using floats.

select ((process_size::float*11/(1024*1024*1024))*100)/(4*3600)

However if you care about precise results, you should stay away from approximate data types like float and use numeric instead.