别名postgresql查询中的长重复表达式

Question

当select和where块中使用相同的表达式时，postgresql中有没有办法不重复自己？

select (
    |/(( power((consumption_2011 - consumption_3y/3), 2)
       + power((consumption_2012 - consumption_3y/3), 2)
       + power((consumption_2013 - consumption_3y/3), 2)
    ) / 3)) as deviation
from consumption
where (
    |/(( power((consumption_2011 - consumption_3y/3), 2)
       + power((consumption_2012 - consumption_3y/3), 2)
       + power((consumption_2013 - consumption_3y/3), 2)
    ) / 3) > 0.8
)

Answer 1

你可以这样做：

select deviation 
from (
select 
    (( power((consumption_2011 - consumption_3y/3), 2)
      + power((consumption_2012 - consumption_3y/3), 2)
      + power((consumption_2013 - consumption_3y/3), 2)
    ) / 3) as deviation
from consumption) sub
where deviation > 0.8