我想要有条件的第一个和第二个插入值

Question

Table abc :

Consgno     Name      Entrydatetime

 111          A     01/03/2017 10:10:15
 111          A     01/03/2017 10:20:15
 111          A     01/03/2017 11:10:20
 222          B     02/03/2017 10:10:25
 333          C     06/03/2017 10:10:25
 333          C     07/03/2017 10:10:12
 444          D     04/03/2017 10:10:41
 444          D     04/03/2017 01:10:20
 444          D     06/03/2017 10:10:32
 555          E     05/04/2017 10:10:15

One Consgno has entered ONE more than one time.

When one Consgno is only once, then the first value should come, otherwise the second entered value should come.

I want to output like this:

   Consgno  Name     Entrydatetime
    111      A      01/03/2017 10:20:15
    222      B      02/03/2017 11:10:36
    333      C      07/03/2017 10:10:12
    444      D      04/03/2017 01:10:20
    555      E      05/04/2017 10:10:15

Answer 1

You can use a query like the following:

;WITH MyWindowedTable AS (
   SELECT Consgno, Name, Entrydatetime,
          ROW_NUMBER() OVER (PARTITION BY Consgno
                             ORDER BY Entrydatetime) AS rn,
          COUNT(*) OVER (PARTITION BY Consgno) AS cnt
FROM mytable
)
SELECT Consgno, Name, Entrydatetime
FROM MyWindowedTable
WHERE (cnt = 1 AND rn = 1) OR (cnt > 1 AND rn = 2)

Using windowed version of COUNT :

COUNT(*) OVER (PARTITION BY Consgno)

returns the population, cnt , of each Consgno partition. We can use cnt to properly filter the records returned: in partitions with a population of 1 we get the single record of the partition, whereas in the rest of the cases we get the one having rn = 2 .

Answer 2

Use ROW_NUMBER and COUNT built in functions :

 CREATE TABLE #table1 ( Consgno INT, Name VARCHAR(1), Entrydatetime 
                         DATETIME)

 INSERT INTO #table1 ( Consgno , Name , Entrydatetime )
 SELECT 111,'A','01/03/2017 10:10:15' UNION ALL
 SELECT 111,'A','01/03/2017 10:20:15' UNION ALL
 SELECT 111,'A','01/03/2017 11:10:20' UNION ALL
 SELECT 222,'B','02/03/2017 10:10:25' UNION ALL
 SELECT 333,'C','06/03/2017 10:10:25' UNION ALL
 SELECT 333,'C','07/03/2017 10:10:12' UNION ALL
 SELECT 444,'D','04/03/2017 10:10:41' UNION ALL
 SELECT 444,'D','04/03/2017 01:10:20' UNION ALL
 SELECT 444,'D','06/03/2017 10:10:32' UNION ALL
 SELECT 555,'E','05/04/2017 10:10:15' 

 SELECT Consgno , Name , Entrydatetime 
 FROM 
 (
    SELECT Consgno , Name , Entrydatetime , ROW_NUMBER() OVER (PARTITION BY 
           Consgno ORDER BY Entrydatetime) RNo , COUNT(*) OVER (PARTITION BY 
           Consgno) AS _Count
    FROM #table1
 ) A WHERE ( RNo = 1 AND _Count = 1) OR (_Count > 1 AND RNo = 2 )