Mysql按一个字段分组，按另一个字段排序

也许这个问题是重复的，但我找不到我的任务的答案。我有下一个表，其中包含以下数据：

我需要为每个oid选择具有唯一oid和最大日期的数据。我有这些查询，但它们工作不正确：

SELECT `oid`, `pvalue`, `date`
FROM `report`
WHERE `deviceid` = 'MRA-1011'
  AND `date` <= '2012-01-20 00:00:00'
GROUP BY oid
HAVING `date` = MAX(`date`)
ORDER BY `date` DESC;

SELECT `oid`, `pvalue`
FROM `report`
WHERE `deviceid` = 'MRA-1011'
  AND `date` <= '2012-01-20 00:00:00'
GROUP BY oid
ORDER BY `date` DESC;

我想得到这个结果：

SELECT `oid`, `pvalue`
FROM `report` AS `r1`
WHERE `deviceid` = 'MRA-1011'
  AND `date` <= '2012-01-20 00:00:00'
  AND `date` = ( SELECT MAX(`date`) 
                 FROM `report` AS `r2` 
                 WHERE `r1`.`oid` = `r2`.`oid`
               )
;

---

您需要沿以下行使用子选择：

SELECT oid, pvalue FROM report
JOIN (SELECT oid, MAX(date) AS maxDate FROM report r WHERE `deviceid` = 'MRA-1011'
AND `date` <= '2012-01-20 00:00:00' GROUP BY oid) AS foo
ON foo.oid=r.oid AND foo.maxDate = report.date;

---

如果report.date不是唯一的，您可能希望在外部查询中按它分组

以获得该结果，您必须

ORDER BY `date` ASC:

SELECT `oid`, `pvalue`
FROM `report`
WHERE `deviceid` = 'MRA-1011'
AND `date` <= '2012-01-20 00:00:00'
GROUP BY oid
HAVING `date` = MAX(`date`)
ORDER BY `date` ASC;

试试这个：

SELECT `oid`, `pvalue`, `date`, MAX(`date`)
FROM `report`
WHERE `deviceid` = 'MRA-1011'
AND `date` <= '2012-01-20 00:00:00'
GROUP BY oid
HAVING `date` = MAX(`date`)
ORDER BY `date` DESC;

---

请添加这些查询的结果以及您希望从中获得的内容。\@sashi kant，请查看更正我的问题！这里有一个小错误。在定义报表r的括号外不能有r.oid。这不适用于我，因为日期不依赖于分组依据