如何根据版本获取表数据

Question

我有这样的学生表：

最初在版本0中有2条记录。每当我在记录中进行任何更改时，它总是在表中创建具有新记录ID但同样是student_id和新版本的新条目。这是为了版本管理和数据回溯。

现在我运行查询以获取版本0的数据：

SELECT * FROM tblStudent as a
inner join (
select student_id, max(record_id) as MaxRecordID from tblStudent group by student_id
) b on a.student_id=b.student_id and a.record_id = MaxRecordID
where a.version=0 

由于最新的reocord将具有最大record_id所以我按student_id进行分组，并且只获得具有最大record_id的记录。

但它给我错误的输出。问题是我不能在内部联接查询中编写version=0条件而group by student_id。

Answer 1

这就是我所做的。我假设您将该版本作为参数传递给查询。

create table #temp1(
recordid int, 
student_id int,
student_name varchar(5),
version int
)

insert into #temp1
values(1,1,'aaa',0)

insert into #temp1
values(2,2,'bbb',0)

insert into #temp1
values(3,3,'ccc',0)

insert into #temp1
values(4,1,'aa1',1)

insert into #temp1
values(5,1,'aa2',1)


declare @version int = 0;

with cte (recordid, student_id) 
as (select max(recordid) , student_id 
      from #temp1 
      where version <= @version group by student_id
   ) 
select cte.recordId, t.student_id, t.version, t.student_name 
from cte 
inner join #temp1 t on t.recordid = cte.recordid 

Answer 2

您可以使用row_number() over ( partion by Student_Id order by version)。 见example

CREATE TABLE tblStudent(Record_Id INT, Student_Id INT, Student_Name nvarchar(50) , Version INT)

INSERT INTO tblStudent(Record_Id, Student_Id, Student_Name, Version)
VALUES 
(1,1,'aaa',0),
(2, 2, 'bbb', 0),
(3,3,'aaa',0),
(4,1,'aa1',1),
(5,1,'aa2',2)

SELECT *
FROM (
    SELECT *, Row_Number() OVER (PARTITION BY Student_Id ORDER BY Version ASC) Ranking
    FROM tblStudent
) sub
WHERE sub.Ranking = 1

应该更改选择*

如果您想要最新版本，可以使用DESC代替ASC。检查执行计划，根据排序添加正确的索引。

Answer 3

一种非常简单的方法：

create table #t (record_id int, student_id int, student_name varchar(50), version int)
insert into #t values
(1,1,'aaa',0),
(2,2,'bbb',0),
(3,3,'ccc',0),
(4,1,'aa1',1),
(5,1,'aa2',1)

select * from #t

declare @ver int;
set @ver = 1;  --configurable as 0 or 1

SELECT a.* FROM #t as a
inner join (
select student_id, max(record_id) as MaxRecordID from #t group by student_id
) b on a.student_id=b.student_id 
where (
        (@ver = 1 and  (a.record_id = b.MaxRecordID))
        or
        (@ver = 0) and  (a.version = 0)
    )
order by a.student_id

用tblStudent替换#t