Question

包含五个相关字段的表格;

ID (Autoincrement,unique, etc)
ID_customer - ties in each row to another table with customers, not unique, not NULL
value1 - can be 0 and NULL (NULL is not 0)
value2 - can be 0 and NULL (NULL is not 0)
type - can be 1 or 0

我想通过表格查找每个客户有多行的情况，如果有多个行在类型上具有相同的值，请删除其值列中只有0的所有行。例如;

 1 1 40 8 1
 2 1  0 0 1  <--
 3 1 30 5 0
 4 1 45 8 0

在这种情况下，命令需要删除指示的行，但保持其他行不变。不太难。像这样的东西可能会起作用（重复类型= 0）：

DELETE FROM table
WHERE value1 = 0 AND value2 = 0 AND type = 1
   AND ID_customer IN
       (SELECT ID_customer
        FROM table
        WHERE type = 1 GROUP BY ID_customer HAVING count(*) > 1)

问题是这些可能存在的情况：

 5 2 0 0 1
 6 2 0 0 1 <--
 7 2 0 0 0
 8 2 0 0 0 <--

在这种情况下，我想删除两行，但不是所有行。有没有办法让我删除重复行，但只有当值列为0时？这会工作（再次，类型= 0重复），还是我错过了什么？

DELETE
FROM TABLE
WHERE value1 = 0 AND value2 = 0 AND TYPE = 1
  AND ID NOT IN
    (SELECT ID
     FROM TABLE
     WHERE value1 = 0 AND value2 = 0 AND TYPE = 1
     GROUP BY ID_customer)

编辑：我已经查看了其他重复的删除问题，但我找不到以我的表所需的方式定义子查询的问题（我希望保留一些重复项）。

Answer 1

所以对于第一个问题：

您对第一个问题的查询会导致错误（You can't specify target table 'table1' for update in FROM clause

但是，如果使用派生表（嵌套子查询），它可以正常工作：

DELETE
FROM table1
WHERE value1 = 0
    AND value2 = 0
    AND TYPE = 1
    AND ID_customer IN
        (SELECT ID_customer
         FROM
             (SELECT ID_customer
              FROM table1
              WHERE TYPE = 1
              GROUP BY ID_customer
              HAVING count(*) > 0) AS derived)

对于第二个问题，该方法非常相似，但也使用ID字段：

DELETE
FROM table1
WHERE ID IN
        (SELECT dups.ID
         FROM
             (SELECT t1.ID
              FROM table1 t1
              JOIN table1 t2 ON t1.ID_Customer = t2.ID_Customer
              AND t1.value1 = t2.value1
              AND t1.value2 = t2.value2
              AND t1.type = t2.type
              AND t1.ID > t2.ID
              WHERE t1.value1 = 0
                  AND t2.value2 =0 ) AS dups);

希望这有帮助。

如何删除MySQL表中的“额外”空白行？

1 个答案: