PostgreSQL視圖：引用另一個計算字段中的一個計算字段

Question

我有與#1895500相同的問題，但使用PostgreSQL而不是MySQL。

我如何定義，有一個計算的字段，例如一個觀點：

(mytable.col1 * 2) AS times_two 

...並打造了基於第一彼此計算字段：

(times_two * 2) AS times_four 

.. 。？

Answer 1

根據formla是多麼沉重，你可以使用子查詢：

select inner.*, times_two * 2 from 
(select mycol * 2 as times_two from table) sub 

或重寫計算：

select mycol * 2, mycol * 2 * 2 from table 

Answer 2

此語句

 
CREATE VIEW view_name as SELECT column_name*2 as new_col1 , column_name*4 as new_col2 from table_name ; 

select * from view_name ; 

If you want use this view column values. use following things 

create view new_viwe as select new_col1*2 as final_column from view_name ; 

select * from new_view ;