如何通过sql查询每个用户的最新记录日期
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18-09-2019 - |
题
我有一个表,其中包含有关用户登录时间的集合条目。
username, date, value
--------------------------
brad, 1/2/2010, 1.1
fred, 1/3/2010, 1.0
bob, 8/4/2009, 1.5
brad, 2/2/2010, 1.2
fred, 12/2/2009, 1.3
etc..
如何创建一个查询来为我提供每个用户的最新日期?
更新: 我忘记了我需要有一个与最新日期一致的值。
解决方案
select t.username, t.date, t.value
from MyTable t
inner join (
select username, max(date) as MaxDate
from MyTable
group by username
) tm on t.username = tm.username and t.date = tm.MaxDate
其他提示
使用窗口函数(在Oracle,Postgres的8.4,SQL Server 2005的,DB2中,Sybase,火鸟3.0,MariaDB的10.3作品)
select * from (
select
username,
date,
value,
row_number() over(partition by username order by date desc) as rn
from
yourtable
) t
where t.rn = 1
我看到大部分的开发使用嵌入式查询,而不考虑其对海量数据的影响。
简单地说,可以通过实现这一点:
SELECT a.username, a.date, a.value
FROM myTable a
LEFT OUTER JOIN myTable b
ON a.username = b.username
AND a.date < b.date
WHERE b.username IS NULL
ORDER BY a.date desc;
要获取包含该用户的最大日期整行:
select username, date, value
from tablename where (username, date) in (
select username, max(date) as date
from tablename
group by username
)
SELECT *
FROM MyTable T1
WHERE date = (
SELECT max(date)
FROM MyTable T2
WHERE T1.username=T2.username
)
从我的经验,最快的方法是采取其中有表中没有新行的每一行。下面是一些数据我手边一点基准。
另一个优点是,所使用的语法是很简单的,并且该查询的意义是相当容易掌握(采取所有的行,使得没有更新的行存在的用户名被考虑)。
NOT EXISTS
SELECT username, value
FROM t
WHERE NOT EXISTS (
SELECT *
FROM t AS witness
WHERE witness.date > t.date
);
解释总成本:2.38136
ROW_NUMBER
SELECT username, value
FROM (
SELECT username, value, row_number() OVER (PARTITION BY username ORDER BY date DESC) AS rn
FROM t
) t2
WHERE rn = 1
总成本:61.5823
INNER JOIN
SELECT t.username, t.value
FROM t
INNER JOIN (
SELECT username, MAX(date) AS date
FROM t
GROUP BY username
) tm ON t.username = tm.username AND t.date = tm.date;
解释总成本:67.5439
LEFT OUTER JOIN
SELECT username, value
FROM t
LEFT OUTER JOIN t AS w ON t.username = w.username AND t.date < w.date
WHERE w.username IS NULL
解释总成本:62.964
在解释计划来自用约10K行的数据库,存储为XML。还使用的查询包含谓词 “GROUP_ID = '1'”。
这应该给你正确的结果为您编辑的问题。
在子查询可确保找到最新的日期仅排,外GROUP BY
将关系照顾。当有在同一日期为同一用户的两个条目,它将返回一个具有最高value
。
SELECT t.username, t.date, MAX( t.value ) value
FROM your_table t
JOIN (
SELECT username, MAX( date ) date
FROM your_table
GROUP BY username
) x ON ( x.username = t.username AND x.date = t.date )
GROUP BY t.username, t.date
您也可以使用分析秩函数
with temp as
(
select username, date, RANK() over (partition by username order by date desc) as rnk from t
)
select username, rnk from t where rnk = 1
SELECT Username, date, value
from MyTable mt
inner join (select username, max(date) date
from MyTable
group by username) sub
on sub.username = mt.username
and sub.date = mt.date
将解决更新问题。它可能不是大表上工作这么好,即使有良好的索引。
SELECT *
FROM ReportStatus c
inner join ( SELECT
MAX(Date) AS MaxDate
FROM ReportStatus ) m
on c.date = m.maxdate
对于Oracle排序结果降序排列设置,并采取的第一条记录,所以你会得到的最新记录:
select * from mytable
where rownum = 1
order by date desc
SELECT t1.username, t1.date, value
FROM MyTable as t1
INNER JOIN (SELECT username, MAX(date)
FROM MyTable
GROUP BY username) as t2 ON t2.username = t1.username AND t2.date = t1.date
Select * from table1 where lastest_date=(select Max(latest_date) from table1 where user=yourUserName)
内部查询将返回当前用户的最新日期,外部查询将根据内部查询结果拉的所有数据。
我用这样的方式把最后一条记录为我有我的表中的每个用户。 这是一个查询来获取最后的位置业务员按在PDA设备上检测到最近的时间。
CREATE FUNCTION dbo.UsersLocation()
RETURNS TABLE
AS
RETURN
Select GS.UserID, MAX(GS.UTCDateTime) 'LastDate'
From USERGPS GS
where year(GS.UTCDateTime) = YEAR(GETDATE())
Group By GS.UserID
GO
select gs.UserID, sl.LastDate, gs.Latitude , gs.Longitude
from USERGPS gs
inner join USER s on gs.SalesManNo = s.SalesmanNo
inner join dbo.UsersLocation() sl on gs.UserID= sl.UserID and gs.UTCDateTime = sl.LastDate
order by LastDate desc
SELECT * FROM TABEL1 WHERE DATE= (SELECT MAX(CREATED_DATE) FROM TABEL1)
我的小合集
- 自己
join
比嵌套更好select
- 但
group by
不给你primary key
这更适合join
- 该密钥可以由以下方式给出
partition by
和这个结合first_value
(文档)
所以,这是一个查询:
select t.* from Table t inner join ( select distinct first_value(ID) over(partition by GroupColumn order by DateColumn desc) as ID from Table where FilterColumn = 'value' ) j on t.ID = j.ID
优点:
- 过滤数据
where
使用任意列的语句 select
过滤行中的任何列
缺点:
- 从 2012 年开始需要 MS SQL Server。
我确实有点为我的,因为它的应用程序:
下面是查询:
select distinct i.userId,i.statusCheck, l.userName from internetstatus
as i inner join login as l on i.userID=l.userID
where nowtime in((select max(nowtime) from InternetStatus group by userID));
这是类似于上面的答案之一,但在我看来,这是一个非常简单并且整洁。此外,显示了良好的使用了交叉应用陈述。对于SQL Server 2005及以上...
select
a.username,
a.date,
a.value,
from yourtable a
cross apply (select max(date) 'maxdate' from yourtable a1 where a.username=a1.username) b
where a.date=b.maxdate
SELECT DISTINCT Username, Dates,value
FROM TableName
WHERE Dates IN (SELECT MAX(Dates) FROM TableName GROUP BY Username)
Username Dates value
bob 2010-02-02 1.2
brad 2010-01-02 1.1
fred 2010-01-03 1.0
这也应该工作,以获得所有最新的条目,为用户。
SELECT username, MAX(date) as Date, value
FROM MyTable
GROUP BY username, value
您将使用聚合函数MAX和GROUP BY
SELECT username, MAX(date), value FROM tablename GROUP BY username, value