Question

I’m searching for the solution since hours, but cat get it.

My table:

ID         name          value1      value2
1          Meyer         20          _
2          Schmitt       20          _
3          Berger        _           20
4          Chief         _           20

my query:

SELECT A.ID, A.name AS nameA, B.name AS nameB, A.value1 
FROM table AS A INNER JOIN table AS B
ON A.value1 = B.value2

result:

ID      nameA      nameB       value1
1       Meyer      Berger      20
1       Meyer      Chief       20
2       Schmitt    Berger      20
2       Schmitt    Chief       20  

This should look like:

ID      nameA       nameB      value1
1       Meyer       Berger     20
2       Schmitt     Chief      20

How can I get this result?

I also tried the GROUP BY A.name, but get the wrong result:

ID       nameA      nameB     value1
1        Meyer      Berger    20
2        Schmitt    Berger    20

Answer 1

You have not specified DBMS. This is tested in SQL Server:

with C as
(
  select *,
         row_number() over(partition by value1 order by ID) as rn1,
         row_number() over(partition by value2 order by ID) as rn2
  from YourTable
)
select A.ID, 
       A.name as nameA, 
       B.name as nameB, 
       A.value1  
from C as A
  inner join C as B
    on A.value1 = B.value2 and
       A.rn1 = B.rn2

Testable sample:

declare @T table
(
  ID int,
  name varchar(10),
  value1 int,
  value2 int
)
insert into @T values
(1,          'Meyer',         20,          null),
(2,          'Schmitt',       20,          null),
(3,          'Berger',        null,        20),
(4,          'Chief',         null,        20)

;with C as
(
  select *,
         row_number() over(partition by value1 order by ID) as rn1,
         row_number() over(partition by value2 order by ID) as rn2
  from @T
)
select A.ID, 
       A.name as nameA, 
       B.name as nameB, 
       A.value1  
from C as A
  inner join C as B
    on A.value1 = B.value2 and
       A.rn1 = B.rn2