Question

假设我有以下两个条目：

`id`     |    `timestamp`   |   `content`   |  `reference`
 1       |     2012-01-01   |    NEWER      |   1
 2       |     2013-01-01   |    NEWEST     |   1
 3       |     2011-01-01   |    OLD        |   2

我的查询需要以下结果：

`id`     |    `timestamp`   |   `content`   |  `reference`
 2       |     2013-01-01   |    NEWEST     |   1
 3       |     2011-01-01   |    OLD        |   2

这是我到目前为止所做的，但它是不正确的：

SELECT * FROM table GROUP BY reference

这里的正确查询是什么？

我希望获得每个引用ID的最新content段。在上面的示例中，有两个引用ID（1＆amp; 2），我想获取每个引用ID的最新条目。

Answer 1

SELECT * 
FROM (SELECT * FROM table ORDER BY timestamp desc) as sub
GROUP BY reference

如果您希望扩展查询，请将限制逻辑放入子查询中，以获得更好的性能：

SELECT * 
FROM (SELECT * 
      FROM table 
      WHERE 1=1 and 2=2
      ORDER BY timestamp desc
     ) as sub
GROUP BY reference

Answer 2

我认为你想要每个参考的最新版本？像这样：

SELECT * FROM my_table
WHERE id IN (
  SELECT id FROM my_table ORDER BY timestamp DESC GROUP BY reference LIMIT 1
);

Answer 3

select * from table where reference_id in 
    (select max(id) from table group by reference)

mysql中的GROUP BY max

3 个答案: