涉及CTE，CASE和子查询的SQL Server查询

Question

These are the data sets that I am using:

create table test (
masterid int, 
subID varchar(100),
entrydate datetime
)

insert into test
values 
(1,'A','5/1/14'),
(1,'B','4/1/14'),
(1,'C','3/1/14'),
(2,'D','4/1/14'),
(2,'E','6/1/14'),
(2,'F','2/1/14'),
(3,'A','12/1/13'),
(3,'B','1/1/14'),
(3,'E','2/1/14');


Create table test2 (
subID varchar(50),
corptype varchar(50)
)

insert into test2 
values
('A','N'),
('B','N'),
('C','Y'),
('D','Y'),
('E','N'),
('F','N')

    select t1.masterid
           , t1.subID 
           , t2.corptype
           , t1.entrydate
    from   test t1
           join test2 t2 on t1.subID = t2.subID 

I have to write a query with the following requirements:

1.) For a given masterID, if the corptype of any of the subIDs is 'Y', then select the masterID, subID, corptype, and entrydate.

2.) For a masterID that has no 'Y' for any of the subIDs, I need to select the masterID, subID, corptype, and entrydate having the most recent entrydate.

Please assume that the list of masterIDs is too long to identify all Y's first, then select 'N's that don't have a masterID in the list of Y's.

My attempt:

    WITH cte AS
                (
                   SELECT *,
                         ROW_NUMBER() OVER (PARTITION BY t1.masterid ORDER BY t1.entrydate DESC) AS rn
                   FROM test t1
                )

    select CASE (test2.corptype)
    when 'Y'

    THEN

                (select t1.masterid
                        , t1.subID 
                        , t2.corptype
                        , t1.entrydate
                from test t1
                join test2 t2 on t1.subID = t2.subID 
                where t2.corptype = 'Y')

    ELSE            

                (SELECT cc.masterid, cc.subID, t2.corptype, cc.entrydate
                FROM cte cc
                join test2 t2 on cc.subID = t2.subID 
                WHERE rn = 1
                and t2.corptype = 'N'
                --order by cc.entrydate
                )

    END

The final output should be:

masterid    subID corptype    entrydate
1           C      Y            00:00.0
2           D      Y            00:00.0
3           E      N            00:00.0

Answer 1

If I understand correctly, this is a strange sort of prioritization problem. It seems strange because the priorities are coming from two tables. First corptype from test2 and then entrydate from test .

You can solve this genre of problems using row_number() . If I'm correct, then this may do what you want:

select t.masterId, t.smallId, t.corptype, t.entrydate
from (select t.masterID, t.smallID, t2.corptype, t.entrydate,
             row_number() over (partition by t.masterId
                                order by (case when t2.corptype = 'Y' then 0 else 1 end),
                                         t.entrydate desc
                              ) as seqnum
     from test t join
          test2 t2
          on t.smallid = t2.smallid
    ) t
where seqnum = 1;

Answer 2

Select a.MasterId, coalesce(b.subId, c.subId),
   a.entrydate,  
From test a
   Left join test2 b 
      on b.subID = a.subID
         and b.corptype = 'Y'
  join test2 c 
      on c.subID = a.subID
         and a.entryDate =
             (Select Max(entryDate)
              from test 
              where MasterId = a.MasterId)