使用别名在选择查询

Question

我要问，如何能在SELECT查询中使用别名，

我需要这个

SELECT (Complex SubQuery) AS A, (Another Sub Query WHERE ID = A) FROM TABLE 

Answer 1

你不能做到这一点：

SELECT (Complex SubQuery) AS A, (Another Sub Query WHERE ID = A) FROM TABLE 

但是，您可以做此：

SELECT (Another Sub Query WHERE ID = A.somecolumn) 
FROM table 
JOIN SELECT (Complex SubQuery) AS A on (A.X = TABLE.Y) 

或

SELECT (Another Sub Query) 
FROM table 
WHERE table.afield IN (SELECT Complex SubQuery.otherfield) 

问题在于，您不能在SELECT和WHERE子句中引用像这样的别名，因为它们不会在执行select或where部分时进行评估。
也可以使用having子句，但子句不使用索引，应尽可能避免。

Answer 2

你可以重写查询这样

SELECT Complex.A, (Another Sub Query WHERE ID = Complex.A) 
FROM TABLE 
CROSS JOIN ((Complex SubQuery) AS A) Complex 

Answer 3

另一种解决方案，您可以使用：

SELECT (Complex SubQuery) AS A, (Another Sub Query WHERE ID = A) 
FROM 
TABLE MAIN 
OUTER APPLY (SELECT (Complex SubQuery) AS A)