Question

我正在尝试根据客户电话号码从表中删除重复项。下面的内部选择查询正确选择了我需要删除的所有重复记录，但是outter delete查询会生成以下错误：

You can't specify target table 'customers' for update in FROM clause

查询：

DELETE FROM customers WHERE id IN (SELECT id from customers GROUP BY phone HAVING COUNT(phone) > 1)

Answer 1

在update和delete语句中，您通常无法引用要修改的表。一个简单的解决方案是使用join：

DELETE c
    FROM customers c JOIN
         (SELECT phone, COUNT(*) as cnt
          FROM customers c
          GROUP BY phone
         ) p
         ON c.phone = p.phone AND cnt > 1;

请注意，这会从表中删除所有重复项。通常，您希望保留其中一个：

DELETE c
    FROM customers c LEFT JOIN
         (SELECT phone, MIN(id) as minid
          FROM customers c
          GROUP BY phone
         ) p
         ON c.id = p.minid
    WHERE p.phone IS NULL;

删除重复项的查询生成错误

1 个答案: