Question

Currently, I have two MySQL tables.

First table stores relation between the friend and his picture.

TABLE 1

 id  |  pic_id  |  friend_id
----------------------------
 0   |  123     |  84589
 1   |  290     |  11390
 2   |  884     |  84589
 3   |  456     |  84589
 4   |  123     |  11111
 5   |  456     |  22222

TABLE 2

Second table stores more information about the pic…

id   |  pic_id  |  title   |  color  |  detail
----------------------------------------------
0    |  123     | hello    |  black  |  brush
1    |  124     | world    |   red   |  paint
2    |  884     | sample   |  green  |  star

I use JOIN to grab the information I need…

But what if I want to use the pic_id’s that were matched by the above SQL and find OTHER friend_id’s with the same pic_id?

For example, the above SQL command will give me rows 0, 2, and 3 with pic_id’s 123, 884, 456. What SQL command should I use to loop through these pic_id’s and grab associated friend_id’s? I want to end up with 11111 for pic_id 123 and 22222 for pic_id 456.

I have used the following code to accomplish the above. It does not look efficient and is slow though.

$sql = "SELECT b.title, b.color, b.detail
FROM table1 a INNER JOIN table2 b
on a.pic_id = b.pic_id
WHERE friend_id = 84589";

$res = mysqli_query($link,$sql);
    if($res){
        while ($rec = mysqli_fetch_assoc($res)){
            $pic_id.=$rec['pic_id'].",";
            $arr[] = $rec;
        }
    } 

$each_id = explode(',',$pic_id);
    foreach($each_id as $key => $value){
        if ($value){
            $next_sql = "SELECT friend_id FROM table1 WHERE pic_id=".$value;
            $next_res = mysqli_query($link,$next_sql);

            if ($next_res){
                while($next_rec = mysqli_fetch_assoc($next_res)){
                    //do things
                }
            }
        }
    }       

Sorry if this is unclear. Please let me know and I will clarify.

All help is greatly appreciated!

Answer 1

Try this (Updated) :

SELECT a.friend_id, a.pic_id
 FROM table1 a 
  WHERE EXISTS (SELECT 1 FROM table1 t 
          WHERE t.pic_id = a.pic_id AND t.friend_id = 84589)

check this – http://sqlfiddle.com/#!3/91cdf/3