从表中选择最新版本（MS SQL Server、SQLite）

比方说，我有下表：

ID | UID | Version | Content
---+-----+---------+-----------------------------
 1 |   1 |       1 | Something
 2 |   1 |       2 | Something (changed)
 3 |   2 |       1 | Alice has a cat
 4 |   2 |       2 | Alice has a cat and a dog
 5 |   2 |       3 | Alice has a cat and a canary

我需要创建查询，它将返回所有对象，但只返回最新版本的对象，因此在本例中：

ID | UID | Version | Content
---+-----+---------+-----------------------------
 2 |   1 |       2 | Something (changed)
 5 |   2 |       3 | Alice has a cat and a canary

由于SQL方言不同，我将在MS SQL Server 2008和SQLite 3上运行此查询

---

如何实现此目标？

不存在

查询：

select *
from tablename t1
where not exists (select 1 from tablename t2
                  where t2.uid = t1.uid
                    and t2.version > t1.version)

select t1.*
from tablename t1
    join (select uid, max(version) as version from tablename group by uid) t2
    on t2.uid = t1.uid and t2.version = t1.version

加入

查询：

select *
from tablename t1
where not exists (select 1 from tablename t2
                  where t2.uid = t1.uid
                    and t2.version > t1.version)

select t1.*
from tablename t1
    join (select uid, max(version) as version from tablename group by uid) t2
    on t2.uid = t1.uid and t2.version = t1.version

相关子查询：

select t1.*
from tablename t1
where t1.version = (select max(version) from tablename t2
                    where t2.uid = t1.uid)

select *
from tablename
where (uid, version) IN (select uid, max(version) from tablename
                         group by uid)

子查询中的

：

select t1.*
from tablename t1
where t1.version = (select max(version) from tablename t2
                    where t2.uid = t1.uid)

select *
from tablename
where (uid, version) IN (select uid, max(version) from tablename
                         group by uid)

有几种不同的方法来解决这个问题。但每种方法都遵循相同的原则

查询的一部分将标识每个UID的最新版本。这将用于过滤记录集

在下面的示例中，我使用一个子查询找到了每个UID的当前版本，然后用它过滤主记录集