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SQL Query - Get Most Recent Revision

开发者 https://www.devze.com 2022-12-12 15:59 出处:网络
I\'m using T-Sql with SQL Server 2008.Say I have parent table: Projects: ProjectIDProjectNam 1Test Project 1

I'm using T-Sql with SQL Server 2008. Say I have parent table:

Projects:

ProjectID  ProjectNam
1          Test Project 1
2          Test Project 2

and child table ProjectRevisions:

ProjectRevID ProjectID DateCreated
11           1         10/15/2009
12           1         1开发者_C百科0/19/2009
13           1         10/25/2009
21           2         10/05/2009

How do I end up with the most recent ProjectRevision for each Project? Like this:

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


The query below will work regardless of any relationship between ProjectRevId and DateCreated.

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


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

assuming that ProjectRevID and DateCreated are both "going in the same direction" i.e. the next revision receives a higher ID than the previous one.

Joining from Projects allows you to access other columns from Projects, if need be.


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
  )
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