Question

I’m confused on how to write the following query in MySQL: Given one collaborator, I’d like to get all the collaborators that participated on each item that this collaborator worked on.

Here’s my collaborators table:

id collaborator_id item_id
1      1              1
2      2              1
3      3              1
4      4              2
5      1              2
6      2              3

for collaborator_id=1, the query would return:

collaborator_id    item_id
       1              1
       2              1
       3              1
       1              2
       4              2

So collaborator_id=1 worked with collaborator_ids=2,3 on item_id=1 and worked by themselves on item_id=2.

This seems super simple but I’m having a brain freeze on how to get these results. Thoughts?

Answer 1

This query joins on the item_id and gets you all the unique collaborators who worked with a given collaborator on shared items, other than the collaborator himself:

SELECT distinct b.collaborator_id, b.item_id
FROM collab_table a
    JOIN collab_table b
    on a.item_id = b.item_id
WHERE a.collaborator_id = 1
    and b.collaborator_id != 1