为什么该查询没有按我预期的那样工作?
问题描述：
SELECT 3 AS x, 5 as y, (x+y) as z
结果如我所愿；
x y z
3 5 8
我得到的结果；
#1054 - Unknown column 'x' in 'field list'
答
SELECT 子句(和列别名)是同时计算的，没有特定的顺序.也就是说，在你想要 z 的同一点，x 和 y 列还不存在.
The SELECT clause (and column aliases) are evaluated at the same time and in no particular order. That is, at the same point you want z, the columns x and y do not exist yet.
SELECT
(x+y) as z
FROM
(
SELECT 3 AS x, 5 as y
) t;