我正在使用SQL Server,我有一个包含以下列的表:
SessionId | Date | first name | last name
我想group by sessionId
,然后获取最大日期的行。
例如:
xxx | 21/12/2012 | f1 | l1
xxx | 20/12/2012 | f2 | l2
yyy | 21/12/2012 | f3 | l3
yyy | 20/12/2012 | f4 | l4
我想获得以下行:
xxx | 21/12/2012 | f1 | l1
yyy | 21/12/2012 | f3 | l3
谢谢
答案 0 :(得分:5)
试试这个:
WITH MAXSessions
AS
(
SELECT
*,
ROW_NUMBER() OVER(PARTITION BY SessionID ORDER BY Date DESC) rownum
FROM Sessions
)
SELECT
SessionId,
Date,
firstname,
lastname
FROM MAXSessions
WHERE rownum = 1;
或强>
SELECT
s.SessionId,
s.Date,
s.firstname,
s.lastname
FROM Sessions s
INNER JOIN
(
SELECT SessionID, MAX(Date) LatestDate
FROM sessions
GROUP BY SessionID
) MAxs ON maxs.SessionID = s.SessionID
AND maxs.LatestDate = s.Date;
更新:要获取会话次数,您可以执行以下操作:
SELECT
s.SessionId,
s.Date,
s.firstname,
s.lastname,
maxs.SessionsCount
FROM Sessions s
INNER JOIN
(
SELECT SessionID, COUNT(SessionID), SessionsCount, MAX(Date) LatestDate
FROM sessions
GROUP BY SessionID
) MAxs ON maxs.SessionID = s.SessionID
AND maxs.LatestDate = s.Date;
答案 1 :(得分:3)
以下是Mahmoud的答案 - SQL Fiddle
的实例以下是相同的,只使用子查询:
SELECT a.*
FROM
#Table a
INNER JOIN
(
SELECT
SessionID,
[mx] = MAX([Date])
FROM #Table
GROUP BY SessionID
) b
ON
a.[SessionId ] = b.SessionID AND
a.[Date] = b.mx;
HERE IS THE SQL FIDDLE FOR THE ABOVE SUB-QUERY VERSION
你也可以使用EXISTS
- 这是我的最爱:
SELECT
a.*,
c.CNT
FROM
#Table a
INNER JOIN
( --to return a count of sessionIds
SELECT
SessionID,
[CNT] = COUNT(*)
FROM #Table
GROUP BY SessionID
) c
ON a.SessionID = c.SessionID
WHERE
EXISTS
(
SELECT 1
FROM #Table b
WHERE
a.[SessionId] = b.SessionID AND
a.[Date] > b.[Date]
)
答案 2 :(得分:0)
一些选项,一种是使用按日期对行进行排名的CTE:
已修改为包含会话计数
WITH Sessions AS (
SELECT SessionId, [Date], FirstName, LastName,
ROW_NUMBER() OVER (PARTITION BY SessionId ORDER BY [Date] DESC) AS Ord
FROM YourTable
)
SELECT S.SessionId, S.Date, S.FirstName, S.LastName, X.SessionCount
FROM Sessions S
INNER JOIN (
SELECT SessionId, COUNT(*) AS SessionCount
FROM Sessions
GROUP BY SessionId
) X ON X.SessionId = S.SessionId
WHERE S.Ord = 1
在这种情况下,Ranking Functions是您的朋友,您希望获取满足某些“有序”条件的整行,例如最大日期。
答案 3 :(得分:0)
我们走了,这就是
select a.date1,a.first_name,a.last_name
from(select row_number()
over(partition by SessionId order by SessionId) rnk,date1,first_name,last_name
from table1) a where a.rnk=1
答案 4 :(得分:0)
SELECT b.sessionid,
b.date,
b.fristname, b.lastname
FROM (SELECT t2.sessionid,
Max(t2.date) AS Date
FROM temp1 t2
GROUP BY t2.sessionid) a,
temp1 b
WHERE a.sessionid = b.sessionid
AND a.date = b.date
找到结果的最佳方式是