Question

我有一张表，我需要将总行数保持在50,000以内。该表包含Id字段（id为自动增量）。

如何查看是否max(id) - min(id) > 50,000，然后删除之前的行？

DELETE FROM news WHERE if (max(id) - min(id) > 50000)

如果query，此max(id) - min(id) > 50000会删除所有行，这是正确的方法吗？理想情况下，我需要一个单行命令，借口用SSH方法。感谢。

Answer 1

DELETE d 
FROM news AS d
  JOIN
    ( SELECT MAX(id)-50000 AS lim 
      FROM news
    ) AS m
    ON d.id < m.lim ;

由于id序列中可能存在间隙，因此上述内容当然不会留下50K行。但我想这是预料而不是问题。如果你真的想要留下50K行，那么任何语句都可能效率低下。你可以尝试这个：

DELETE d 
FROM news AS d
  JOIN
    ( SELECT id AS lim 
      FROM news
      ORDER BY id DESC
      LIMIT 1 OFFSET 50000
    ) AS m
    ON d.id <= m.lim ;

Answer 2

Delete from news where id < max(id)-50000

Answer 3

DELETE FROM news 
WHERE id NOT IN (SELECT id FROM news ORDER BY id DESC LIMIT 50000)

如果max（id） - min（id）＆gt; mysql删除早期数据50000

3 个答案: