一條語句簡單解決“每個Y的最新X”的經(jīng)典sql語句
發(fā)布日期：2022-02-03 12:44 | 文章來源：源碼中國
復(fù)制代碼 代碼如下:
/******創(chuàng)建表******/
ifexists(select*fromdbo.sysobjectswhereid=object_id(N'[dbo].[Table]')andOBJECTPROPERTY(id,N'IsUserTable')=1)
droptable[dbo].[Table]
GO
CreateTABLE[dbo].[Table](
[ID][int]IDENTITY(1,1)NOTNULL,
[Y][nvarchar](50)COLLATEChinese_PRC_CI_ASNOTNULL,
[X][smalldatetime]NOTNULL
)ON[PRIMARY]
GO
--插入數(shù)據(jù)
InsertINTO[Table](Y,X)values('CCC','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('AAA','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('AAA','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('BBB','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('BBB','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('BBB','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('CCC','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('AAA','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('CCC','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('DDD','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('DDD','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('DDD','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('EEE','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('EEE','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('EEE','2007-03-0303:03:03')
GO /******創(chuàng)建表******/
ifexists(select*fromdbo.sysobjectswhereid=object_id(N'[dbo].[Table]')andOBJECTPROPERTY(id,N'IsUserTable')=1)
droptable[dbo].[Table]
GO
CreateTABLE[dbo].[Table](
[ID][int]IDENTITY(1,1)NOTNULL,
[Y][nvarchar](50)COLLATEChinese_PRC_CI_ASNOTNULL,
[X][smalldatetime]NOTNULL
)ON[PRIMARY]
GO
--插入數(shù)據(jù)
InsertINTO[Table](Y,X)values('CCC','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('AAA','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('AAA','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('BBB','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('BBB','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('BBB','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('CCC','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('AAA','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('CCC','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('DDD','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('DDD','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('DDD','2007-03-0303:03:03')
InsertINTO[Table](Y,X)values('EEE','2007-01-0101:01:01')
InsertINTO[Table](Y,X)values('EEE','2007-02-0202:02:02')
InsertINTO[Table](Y,X)values('EEE','2007-03-0303:03:03')
GO解決“每個Y的最新X”經(jīng)典SQL問題：以下幾種方法真是八仙過海
復(fù)制代碼 代碼如下:
SelectID,Y,X
FROM[Table]T1
Where(NOTEXISTS
(Select1
FROM[Table]T2
Where(T2.Y=T1.Y)AND(T2.X>T1.Xor
T2.X=T1.XANDT2.ID>T1.ID)))
/*****************************************************************************/
Select*
FROM[Table]
WhereIDIN
(SelectMAX(T1.ID)
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)
/*****************************************************************************/
SelectT.ID,T.Y,T.X
FROM[Table]TINNERJOIN
(SelectMAX(T1.ID)ASID
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)T2ONT.ID=T2.ID
/*****************************************************************************/
Select*
FROM[Table]T1
WhereIDIN
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC)
/*****************************************************************************/
Select*
FROM[Table]T1
Where(ID=
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC,IDDESC))
/*****************************************************************************/ /*****************************************************************************/
SelectID,Y,X
FROM[Table]T1
Where(NOTEXISTS
(Select1
FROM[Table]T2
Where(T2.Y=T1.Y)AND(T2.X>T1.Xor
T2.X=T1.XANDT2.ID>T1.ID)))
/*****************************************************************************/
Select*
FROM[Table]
WhereIDIN
(SelectMAX(T1.ID)
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)
/*****************************************************************************/
SelectT.ID,T.Y,T.X
FROM[Table]TINNERJOIN
(SelectMAX(T1.ID)ASID
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)T2ONT.ID=T2.ID
/*****************************************************************************/
Select*
FROM[Table]T1
WhereIDIN
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC)
/*****************************************************************************/
Select*
FROM[Table]T1
Where(ID=
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC,IDDESC))
FROM[Table]T1
Where(NOTEXISTS
(Select1
FROM[Table]T2
Where(T2.Y=T1.Y)AND(T2.X>T1.Xor
T2.X=T1.XANDT2.ID>T1.ID)))
/*****************************************************************************/
Select*
FROM[Table]
WhereIDIN
(SelectMAX(T1.ID)
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)
/*****************************************************************************/
SelectT.ID,T.Y,T.X
FROM[Table]TINNERJOIN
(SelectMAX(T1.ID)ASID
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)T2ONT.ID=T2.ID
/*****************************************************************************/
Select*
FROM[Table]T1
WhereIDIN
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC)
/*****************************************************************************/
Select*
FROM[Table]T1
Where(ID=
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC,IDDESC))
/*****************************************************************************/ /*****************************************************************************/
SelectID,Y,X
FROM[Table]T1
Where(NOTEXISTS
(Select1
FROM[Table]T2
Where(T2.Y=T1.Y)AND(T2.X>T1.Xor
T2.X=T1.XANDT2.ID>T1.ID)))
/*****************************************************************************/
Select*
FROM[Table]
WhereIDIN
(SelectMAX(T1.ID)
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)
/*****************************************************************************/
SelectT.ID,T.Y,T.X
FROM[Table]TINNERJOIN
(SelectMAX(T1.ID)ASID
FROM[Table]T1JOIN
(Selecty,MAX(x)x
FROM[Table]
GROUPBYy)T2ONT1.Y=T2.YANDT1.x=T2.x
GROUPBYT1.y)T2ONT.ID=T2.ID
/*****************************************************************************/
Select*
FROM[Table]T1
WhereIDIN
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC)
/*****************************************************************************/
Select*
FROM[Table]T1
Where(ID=
(SelectTOP1ID
FROM[Table]
WhereY=T1.Y
orDERBYXDESC,IDDESC))
/*****************************************************************************
/效率嘛,在不同的字段建立索引速度都不盡相同,使用者見仁見智了.
第一種方法速度在各方面都不錯,而且在Y列在建立索引，可以大大優(yōu)化查詢速度。
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