Question

我现在有一张有604 000行的表。我想删掉4000个随机行，所以我的表只包含60万个条目。

会有快速的方法吗？

非常感谢。

Answer 1

从理论上讲，这将是随机而快速的。在实践中，它只会很快：

DELETE FROM tableX
LIMIT 4000

这将是随机但非常慢的，有600K行：

DELETE FROM tableX
ORDER BY RAND() 
LIMIT 4000

这不是真正随机的（因为ids中通常存在间隙），它甚至可能不会删除正好4000行（但是当有很多间隙时会少一些）但它可能比之前更快。

需要在子查询中进行额外的换行，因为从多个表中删除的语法不允许LIMIT：

DELETE td
FROM
      tableX AS td
  JOIN 
      ( SELECT t.id
        FROM
             tableX AS t 
          CROSS JOIN
              ( SELECT MAX(id) AS maxid 
                FROM tableX
              ) AS m
          JOIN
              ( SELECT RAND() AS rndm
                FROM tableX AS tr
                LIMIT 5000
              ) AS r
            ON 
               t.id = CEIL( rndm * maxid )
        LIMIT 4000
      ) AS x
      ON 
         x.id = td.id

解释输出（子查询的输出，来自400K行表）：

id           table        possible_keys  key_len     rows 
 select_type         type             key     ref         Extra
1 PRIMARY <derived2> system                             1
1 PRIMARY <derived3> ALL                             5000
1 PRIMARY t          eq_ref PRIMARY PRIMARY 4 func      1 Using where;Using index
3 DERIVED tr         index          PRIMARY 4      398681 Using index
2 DERIVED                                            Select tables optimized away

Answer 2

delete from yourTable limit 4000

Answer 3

如果我不得不猜测：

DELETE FROM table where id = (SELECT id FROM table ORDER BY rand() LIMIT 1) LIMIT 10

Answer 4

DELETE FROM TABLE ORDER BY RAND() LIMIT 4000;

它需要时间......

更快的执行方式（不是编写代码！）可能是循环中的4000个单独删除

DELETE FROM TABLE WHERE AssumedPKisInt = <ARandomNumber>

当然，您需要确保不要尝试删除不存在或已删除的行。

Mysql从表中删除多个随机行

4 个答案: