Mysql：用什么代替 WITH 语句或 TEMPORARY 表？

Question

有没有办法将 select 查询存储到 table 中？我通常使用 WITH 语句但这只有 mysql 8+ 才有可能。我目前正在使用 mysql 5.1。因此，我尝试实现一个临时 table 但不可能在同一查询中多次引用临时 table（如下面的查询）。

CREATE TEMPORARY TABLE test
SELECT  TIMESTAMPDIFF(MONTH, MAX(L.period), CURDATE()) as timediff, L.contractID 
FROM license L GROUP BY L.contractID;

UPDATE `contract` AS C
SET C.valid = CASE
WHEN (SELECT timediff FROM test AS T WHERE T.contractID = C.contractID) < 1 THEN 2
WHEN (SELECT timediff FROM test AS T WHERE T.contractID = C.contractID) = 1 THEN 1
WHEN (SELECT timediff FROM test AS T WHERE T.contractID = C.contractID) > 1 THEN 0
END;

DROP TEMPORARY TABLE test;

Answer 1

您可以通过将更新表述为连接来立即解决您的问题：

UPDATE contract c
INNER JOIN test t
    ON t.contractID = c.contractID
SET valid = CASE WHEN t.timediff < 1 THEN 2
                 WHEN t.timediff = 1 THEN 1
                 ELSE 0 END;

这种方法解决了多次引用临时 table 的问题。

Mysql：用什么代替 WITH 语句或 TEMPORARY 表？

Mysql: what to use instead of WITH statement or TEMPORARY tables?

mysql

temp-tables