Question

I’m trying to write a simple query in sqlite with a self join. I want all the pairs of IDs of the products that have the same cost, but I want unique pairs (i.e. don’t list the same pair twice even in different order).
Here’s what I’ve got:

SELECT b1.Id, b2.Id
FROM Basic AS b1
LEFT JOIN Basic AS b2
ON b1.cost = b2.cost
WHERE b1.Id != b2.Id
AND b1.Cost = 5;

So I get something like

23 | 101
23 | 205
24 | 103
101 | 23 <-- Duplicate!

I’ve tried different combinations of DISTINCT and GROUP BY but I still getting dupicate pairs:

I’ve tried stuff like

SELECT DISTINCT bp1.Id, bp2.Id …

&
… = 5
GROUP BY bp1.Id, bp2.Id;

How can I get rid of duplicate pairs? Any ideas?

I will appreciate your help!

Answer 1

Change != to < in your WHERE clause to ensure that the lowest ID always comes first:

WHERE b1.Id < b2.Id