在MySQL中使用表別名作為列

Question

我有這樣的查詢：

select a,b, (a+b) as c, (a-b) as d, (a+b)*-1 as e, (a+b)/(a-b) as f from test;

有沒有一種方法可以使用我先前定義的別名作為列，因此它將類似於：

(a+b)/(ab) as f from test 到 c/d as f from test

或其他任何我不會在此查詢中重新編碼任何表達式的解決方案。

Answer 1

使用用戶定義的變量 。

SELECT a,b, 
    @c := (a+b) as c, 
    @d := (a-b) as d, 
    @c*-1 as e, 
    @c/@d as f
FROM test;

Answer 2

select *
from (
 select a,b, (a+b) as c, (a-b) as d, (a+b)*-1 as e, (a+b)/(a-b) as f 
 from test
) s

Answer 3

它們可以有多種方式，但是據我所知，您可以通過使用像這樣的子查詢來實現。 當您將主查詢作為子查詢並根據需要使用它時，您將獲得所有別名作為列。

查看本教程以了解更多內容： http : //www.mysqltutorial.org/mysql-subquery/

select a,b,c,d,e,f form 
 (select a,b, (a+b) as c, (a-b) as d, (a+b)*-1 as e, (a+b)/(a-b) as f from test)
x;