2个连接表的2列之间的mysql max

Question

我有2个表，每个

中有相同的列

我可以创建一个将加入2个表并在2

之间给出最大值的查询

我想出了

SELECT MAX(certificate_number) AS max FROM contacts_cstm
UNION
SELECT MAX(certificate_number) AS max FROM accounts_cstm

但这给了我每个人的最大价值。如何修改此查询以在两者之间给出最大值

由于

Answer 1

使用其他查询进行包装可以解决问题：

SELECT MAX(certificate_number) AS max
FROM (
    SELECT certificate_number FROM contacts_cstm
    UNION
    SELECT certificate_number FROM accounts_cstm
) as CHILD

Answer 2

在MAX()之外调用UNION，而不是在内部。

SELECT MAX(maxnum) AS maxnum FROM
(
  SELECT MAX(certificate_number) as maxnum FROM contacts_cstm
  UNION
  SELECT MAX(certificate_number) as maxnum FROM accounts_cstm
) subq

Answer 3

尝试：

SELECT MAX(m) FROM
    (SELECT MAX(certificate_number) as m FROM contacts_cstm
     UNION
     SELECT MAX(certificate_number) as m FROM accounts_cstm) t

或

SELECT MAX(certificate_number) FROM
    (SELECT certificate_number FROM contacts_cstm
     UNION
     SELECT certificate_number FROM accounts_cstm) t