在MySQL中合并两个UPDATE语句

Question

有没有一种方法可以合并以下两个语句，使我只写一次UPDATE表？该表的名称为STAT_SEP。

UPDATE STAT_SEP LEFT JOIN calendar on STAT_SEP.`Period` = calendar.`Unique_Period`
SET
STAT_SEP.First_Date = calendar.First_Date;

UPDATE STAT_SEP
, (SELECT First_Date AS earliest_date FROM STAT_SEP ORDER BY First_Date ASC LIMIT 1) fancy_alias
SET `Index` = TIMESTAMPDIFF(MONTH, earliest_date, First_Date);

Answer 1

您可以在子查询中计算最早的日期，然后将其用于更新：

UPDATE STAT_SEP s LEFT JOIN
       Calendar c
       ON s.`Period` = c.`Unique_Period` CROSS JOIN
       (SELECT MIN(c2.First_Date) as earliest_date
        FROM STAT_SEP s2 JOIN
             Calendar c2
             ON s2.Period = c.unique_period
       ) c2
    SET s.First_Date = c.First_Date,
        s.Index = TIMESTAMPDIFF(MONTH, c2.earliest_date, c.First_Date);