Question

I have got a problem and I am trying to, but I can’t get it to work.

I have got the following table:

messages

|-------------|----------------|
| senderID    | recipientID    |
|-------------|----------------|
| 4           | 3              |
| 3           | 4              |
| 3           | 423            |
| 18          | 4              |
| 391         | 4              |
| 4           | 19             |
| 3           | 4              |
| 48          | 213            |
| and so      | on ...         |
|-------------|----------------|

Now, I want to get a list of the threads, that means: A list of all persons I wrote messages with. So the problem is, that I have to look that either in the column “senderID” or “recipientID” is my userID (wich is, in this example, 4) and that I “erase” duplicate entries (so I don’t have 2 entries with the other user having the id “3” for example).

I have tried some very strange things with JOIN and GROUP BY, but didn’t get it to work.

May somebody please help me?

Best greetings,

SargTeX

Answer 1

select distinct recipientid
from messages
where senderid = 4
union
select distinct senderid
from messages
where recipientid = 4

In the first clause, using distinct means that each recipient will appear only once; the same is true of the second clause, and using union means that only values distinct to both clauses will appear.