Question

我有一张这样的表

ProjectID    PhaseID   Comment     CommentDate
 1             1        a           2/15/2014
 1             1        b           5/1/2014
 1             2        c           8/15/2014
 1             2        d           1/1/2015
 2             1        e           1/21/2014
 2             2        f           5/15/2014
 2             2        g           1/1/2015

我如何获得每个阶段的每个项目的最新（前1）评论？例如，对于项目1，阶段1，我应该得到“b”和“5/1/2014”

谢谢！

Answer 1

select ProjectID,PhaseID,Comment,CommentDate from 
(select row_number() over(partition by Project_ID,PhaseID order by CommentDate desc) as rn,* from table) a 
where a.rn = 1

Answer 2

这种类型的查询在有标识列时效果最好（并且值总是按顺序插入）但是这样可以得到你需要的东西，假设没有重叠的评论日期

select t.*
from table t
inner join (
    SELECT max(commentDate) as maxDate,
        phaseId,
        projectId
    FROM table
    group by phaseId, projectId
) maxComments on t.phaseId = maxComments.phaseId
   and t.projectId = maxComments.projectId
   and t.commentDate = maxComments.maxDate

SQL为两列选择Top x记录

2 个答案: