MySQL支持嵌套联合？

Question

MySQL版本：5.1.36

(select 
    1 as num) 
union
(
    (select 
        2 as num) 
    union
    (select 
        3 as num))

以上查询会引发语法错误。

MySQL不支持联盟的嵌套？ MySQL文档。对此保持沉默。

Answer 1

我承认我从未尝试过嵌套UNION，可能是因为以下查询是等效的并且可以接受：

(SELECT
    1 AS num) 
UNION
(SELECT
    2 AS num) 
UNION
(SELECT
    3 AS num)