Mysql 如何使用SQL选择列中共享最大值的所有行
我有一张这样的桌子:Mysql 如何使用SQL选择列中共享最大值的所有行,mysql,sql,select,Mysql,Sql,Select,我有一张这样的桌子: +----+---------+---------------------+ | id | user_id | start_date | +----+---------+---------------------+ | 1 | 1 | 2014-02-01 00:00:00 | | 2 | 1 | 2014-01-01 00:00:00 | | 3 | 2 | 2014-01-01 00:00:00 | | 4
+----+---------+---------------------+
| id | user_id | start_date |
+----+---------+---------------------+
| 1 | 1 | 2014-02-01 00:00:00 |
| 2 | 1 | 2014-01-01 00:00:00 |
| 3 | 2 | 2014-01-01 00:00:00 |
| 4 | 2 | 2014-01-01 00:00:00 |
| 5 | 3 | 2015-01-01 00:00:00 |
+----+---------+---------------------+
SELECT t.* FROM ticket t
JOIN (
SELECT start_date, MAX(start_date) FROM ticket /* GROUP BY user_id */
) highest
ON t.start_date = highest.start_date
WHERE t.start_date <= NOW();
如何为每个用户选择具有以下内容的所有行:
开始日期在现在和之前
最长开始日期
因此,对于示例行,输出应为:
+----+---------+---------------------+
| id | user_id | start_date |
+----+---------+---------------------+
| 1 | 1 | 2014-02-01 00:00:00 | // this is a single maximum date within that user
| 3 | 2 | 2014-01-01 00:00:00 | // these two share maximum start date
| 4 | 2 | 2014-01-01 00:00:00 |
+----+---------+---------------------+
到目前为止,我得到的是这样的东西:
+----+---------+---------------------+
| id | user_id | start_date |
+----+---------+---------------------+
| 1 | 1 | 2014-02-01 00:00:00 |
| 2 | 1 | 2014-01-01 00:00:00 |
| 3 | 2 | 2014-01-01 00:00:00 |
| 4 | 2 | 2014-01-01 00:00:00 |
| 5 | 3 | 2015-01-01 00:00:00 |
+----+---------+---------------------+
SELECT t.* FROM ticket t
JOIN (
SELECT start_date, MAX(start_date) FROM ticket /* GROUP BY user_id */
) highest
ON t.start_date = highest.start_date
WHERE t.start_date <= NOW();
但这并没有达到预期效果。我走的路好吗 你的思路是对的。 在派生表中,需要获取每个用户id的最大日期,因此:
SELECT user_id,
MAX(start_date) as MaxDate
FROM ticket
GROUP BY user_id
然后,您可以在开始日期和用户id加入:
SELECT t.* FROM ticket t
JOIN (
SELECT user_id,
MAX(start_date) as MaxDate
FROM ticket
GROUP BY user_id
) highest
ON t.start_date = highest.maxdate
and t.user_id = highest.user_id
WHERE t.start_date <= NOW();
在某种程度上,你走对了方向。 在派生表中,需要获取每个用户id的最大日期,因此:
SELECT user_id,
MAX(start_date) as MaxDate
FROM ticket
GROUP BY user_id
然后,您可以在开始日期和用户id加入:
SELECT t.* FROM ticket t
JOIN (
SELECT user_id,
MAX(start_date) as MaxDate
FROM ticket
GROUP BY user_id
) highest
ON t.start_date = highest.maxdate
and t.user_id = highest.user_id
WHERE t.start_date <= NOW();
_试试这个:
SELECT T.* FROM ticket AS T
JOIN (SELECT
[User_Id]
,MAX([Start_Date]) AS Start_Date
FROM ticket
WHERE Start_Date <= GETDATE()
GROUP BY User_Id) AS Grouped ON T.User_Id = Grouped.User_Id AND T.Start_Date = Grouped.Start_Date
ORDER BY Id
DROP TABLE #This
_试试这个:
SELECT T.* FROM ticket AS T
JOIN (SELECT
[User_Id]
,MAX([Start_Date]) AS Start_Date
FROM ticket
WHERE Start_Date <= GETDATE()
GROUP BY User_Id) AS Grouped ON T.User_Id = Grouped.User_Id AND T.Start_Date = Grouped.Start_Date
ORDER BY Id
DROP TABLE #This