SQL Server：根据两个表中的特定列获取最新记录

Question

我有两个具有相同表格设计的表格。

tblSpeaker1：

--------------------- 
|ID|Speaker |Version| 
|--+--------+-------| 
|B1|Xiong |1  | 
|B1|Ling |2  | 
|B1|Juyng |4  | 
|G4|Micre |1  | 
|G4|Pyong |2  | 
|Y1|Mong |2  | 
--------------------- 

tblSpeaker2：

--------------------- 
|ID|Speaker |Version| 
|--+--------+-------| 
|B1|Looke |3  | 
|G4|Chui |3  | 
|G4|Kyui |4  | 
|Y1|Druke |1  | 
--------------------- 

我想实现的是让基于版本的每个ID的最新记录没有，但没有版本列。

目前，我有这个疑问：

SELECT TOP 1 ID, Speaker 
FROM 
    (SELECT * FROM tblSpeaker1 
    UNION 
    SELECT * FROM tblSpeaker2) 
ORDER BY Version 

但它只返回：

------------- 
|ID|Speaker | 
|--+--------| 
|B1|Juyng | 
------------- 

这应该是输出

------------- 
|ID|Speaker | 
|--+--------| 
|B1|Juyng | 
|G4|Kyui | 
|Y1|Mong | 
------------- 

请帮助我。谢谢。

Answer 1

这是您想要使用PARTITION BY的情况。我给出如下图示：

declare @tblSpeaker1 table 
(
id char(2), 
speaker varchar(10), 
version int 
) 
declare @tblSpeaker2 table 
(
id char(2), 
speaker varchar(10), 
version int 
) 

insert into @tblSpeaker1 VALUES 
('B1','Xiong',1), 
('B1','Ling',2), 
('B1','Juyng',4), 
('G4','Micre',1), 
('G4','Pyong',2), 
('Y1','Mong',2) 

insert into @tblSpeaker2 VALUES 
('B1','Looke',3), 
('G4','Chui',3), 
('G4','Kyui',4), 
('Y1','Druke',1) 

SELECT id, speaker FROM 
(select id, speaker, version, 
ROW_NUMBER() OVER (PARTITION BY id ORDER BY version DESC) as rn from 
(select id, speaker, version FROM @tblSpeaker1 
union 
select id, speaker, version FROM @tblSpeaker2) u) r 
WHERE r.rn = 1 

为了让你明白这里发生了什么。首先你需要将两个表联合起来（就像你在做的那样）。接下来，我们使用row_number（）函数与partition by组合，通过id获得编号，其版本号为desc。最后，我们需要其行号为1。

Answer 2

declare @tbResult table (ID varchar(2), Speaker varchar(50)) 
declare @IDTables table (idx int identity(1,1), ID varchar(20)) 
declare @Counter int 
declare @Categories int 
declare @Speakers table (ID varchar(2), Speaker varchar(50), Version int) 

set @Counter = 1 

insert into @Speakers 
select ID, Speaker, Version from tblSpeaker1 
insert into @Speakers 
select ID, Speaker, Version from tblSpeaker2 

insert into @IDTables 
select distinct ID from tblSpeaker1 
union 
select distinct ID from tblSpeaker2 

set @Categories = (select count(ID) from @IDTables) 

while (@Counter <= @Categories) 
begin 
    declare @ID varchar(2) 
    set @ID = (Select ID from @IDTables where idx = @Counter) 

    insert into @tbResult 
    select top 1 ID, Speaker from @Speakers 
    where ID = @ID order by Version Desc 

    set @Counter = @Counter + 1 
end 


select * from @tbResult 

Answer 3

使用OVER条款这些值：

WITH united AS 
(
    SELECT * 
     FROM (VALUES ('B1', 'Xiong', 1), 
        ('B1', 'Ling', 2), 
        ('B1', 'Juyng', 4), 
        ('G4', 'Micre', 1), 
        ('G4', 'Pyong', 2), 
        ('Y1', 'Mong', 2)) AS tblSpeaker1(ID, Speaker, Version) 
    UNION 
    SELECT * 
     FROM (VALUES ('B1', 'Looke', 3), 
        ('G4', 'Chui', 3), 
        ('G4', 'Kyui', 4), 
        ('Y1', 'Druke', 1)) AS tblSpeaker2(ID, Speaker, Version) 
), 
numbered AS 
(
    SELECT *, row_number() OVER(PARTITION BY ID ORDER BY Version desc) rn 
     FROM united 
) 
SELECT ID, Speaker 
    FROM numbered 
    WHERE rn = 1; 

输出：

ID Speaker 
---- ------- 
B1 Juyng 
G4 Kyui 
Y1 Mong