Question

我正在使用带有SQL Server 2008的T-Sql。假设我有父表：

项目：

ProjectID  ProjectNam
1          Test Project 1
2          Test Project 2

和子表 ProjectRevisions ：

ProjectRevID ProjectID DateCreated
11           1         10/15/2009
12           1         10/19/2009
13           1         10/25/2009
21           2         10/05/2009

如何为每个项目结束最新的ProjectRevision？像这样：

ProjectRevID ProjectID DateCreated
13           1         10/25/2009
21           2         10/05/2009

Answer 1

select x.mProjectRevID, p.ProjectID, p.ProjectNam, x.mDateCreated
from Projects p
inner join
(
   select projectID
   , max(ProjectRevID) as mProjectRevID
   , max(DateCreated) as mDateCreated
   from ProjectRevisions
   group by ProjectID
) x
on x.projectID = p.ProjectID

假设ProjectRevID和DateCreated都“朝着同一方向”，即下一个版本获得的ID高于前一个版本。

如果需要，从项目加入允许您从项目中访问其他列。

Answer 2

无论ProjectRevId和DateCreated之间是否存在任何关系，下面的查询都将有效。

SELECT *
FROM ProjectRevisions
INNER JOIN (
  SELECT ProjectId
    , MAX(DateCreated) AS DateCreated
  FROM  ProjectRevisions
  GROUP BY ProjectId
  ) AS CurrentRevision
  ON CurrentRevision.ProjectId = ProjectRevisions.ProjectId
  AND CurrentRevision.DateCreated = ProjectRevisions.DateCreated

Answer 3

select ProjectRevID, ProjectID, DateCreated
from Projects p
  inner join ProjectRevisions
  on ProjectRevisions.ProjectId = p.ProjectId
where ProjectRevId = (
  select ProjecRevId
  from ProjectRevisions
  where ProjectId = p.ProjectId
  order by DateCreated desc
  limit 1
  )

SQL查询 - 获取最新版本

3 个答案: