Question

I have a table called ‘connections’ with these fields:

entry_id
user_id
connector_id
cat_id

Lets put some rows

    | entry_id | user_id | connector_id |cat_id        |
    |:---------|---------|:------------:|:------------:|
    | 1        |       11|     33       | 1
    | 2        |       13|     11       | 2
    | 3        |        9|     11       | 4
    | 4        |       11|     33       | 6
    | 5        |       33|     11       | 11
    | 6        |        9|     11       | 8

Pseudocode
(using connection between id = 11 and oid = 9)

Select cat_id FROM connections c
if cat_id is between 1 and 5 
   where c.connector_id = id OR c.user_id = id
   AND  c.connector_id = oid OR c.user_id = oid
else if cat_id is greater than 5
   where oid = user_id and id = connector_id

In english;
If the cat_id is between 1 and 5, it should select cat_ids from where oid and id are both in connector_id or user_id, it doesn’t matter which order as long as they are in one or the other, but if the cat_id is greater than 5, it should only select cat_ids where oid is the user_id and id is the connector_id.

Result (for connection between id = 11 and oid = 9)

    | cat_id     | 
    |:-----------|
    | 4          |        
    | 8          |  

One more example:
Result (for connection between id = 33 and oid = 11 )

   | cat_id     | 
   |:-----------|
   | 1          |        
   | 6          |  

Please ask if they’re parts that are not clear.

Answer 1

You should be able to accomplish this by just following your if statements logically. Something like:

Select cat_id FROM connections c
where 
(id between 1 and 5 AND (c.connector_id = id OR c.user_id = id)
   AND  (c.connector_id = oid OR c.user_id = oid)) 
OR id > 5 AND (oid = user_id and id = connector_id)

Note: in agreement with some of the comments – ensure this is what you need to be doing. I made some assumptions about how you intended your logic to be from the pseudo-code, these may be wrong – so please think about it before just copying and pasting. This specifically applies to how you structured your OR / AND in the where clause.