刷sql题的时候出了这么个问题 输入: Person 表: +----+------------------+ | id | email | +----+------------------+ | 1 | [email protected] | | 2 | [email protected] | | 3 | [email protected] | +----+------------------+ 输出: +----+------------------+ | id | email | +----+------------------+ | 1 | [email protected] | | 2 | [email protected] | +----+------------------+ 解释: [email protected]重复两次。我们保留最小的Id = 1。
编写一个 SQL 删除语句来 删除 所有重复的电子邮件,只保留一个id最小的唯一电子邮件。
以 任意顺序 返回结果表。 (注意: 仅需要写删除语句,将自动对剩余结果进行查询)
DELETE
FROM
Person
WHERE
id NOT IN (SELECT min( id ) FROM Person GROUP BY email )
会报错
You can't specify target table 'Person' for update in FROM clause
查了一下更新表的时候
You can't specify target table '表名' for update in FROM clause这样的错误,它的意思是说,不能先select出同一表中的某些值,再update这个表(在同一语句中),即不能依据某字段值做判断再来更新某字段的值。
要经典加一层 select
DELETE
FROM
Person
WHERE
id NOT IN (SELECT * FROM ( SELECT min( id ) FROM Person GROUP BY email ) t)