Question

I have a table with two fields: ID_From, ID_To.

Now the fields are populated like this:

ID_From    ID_To
  1000      2000           
  2000      1000            
  1000      5000            
  3000      2000            
  4000      3000
  5000      1000

What I would like is to query the database the ID of 1000 and then make it return, how many pairs there are. In this case it would return 2. Quering with ID 2000 would return 1. ID 3000 and 4000 would return zero.

Hope I have made it clear enough. Thanks in advance,
Fischer.

Answer 1

SELECT COUNT(*)
FROM myTable a
  JOIN myTable b
    ON a.ID_To = b.ID_From
    AND a.ID_From = b.ID_To
WHERE a.ID_From = 1000 ;