別名在postgresql查詢中長時間重複的表達式

Question

在select和where塊中使用相同的表達式時，postgresql中有沒有辦法重複自己？

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

你可以做這樣的事情：

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