Matching User result with others in MYSQL

I am looking at something like this

   $query = "SELECT catid, userid FROM prod_list WHERE userid = logged-in-user" //user's chosen categories
    $rs_match = mysql_query($query);

    while($data = mysql_fetch_array($rs_match)开发者_如何学Go)
    {
    $match_pattern = $data['catid'];
    echo $match_pattern; //debugging purposes

    Wears id-(1)
    shoes id-(3)
    books id-(4) 

    //Please How can I get and list other users who have the same choices with the logged in user?
    //Thank you

//Exact same choices or rated choices based on match
//Priority should be given to exact results
//100% match results should be displayed on top others follow

    }

---

Something like that

SELECT userid, COUNT(catid) as matches FROM prod_list WHERE catid IN (CATID_ARRAY_HERE) GROUP BY userid ORDER BY matches DESC

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You can do it using nested query:

SELECT DISTINCT userid FROM prod_list WHERE catid NOT IN (
      SELECT catid FROM prod_list WHERE catid NOT IN (

             SELECT catid FROM prod_list WHERE userid = logged-in-user
      ) 
)

The last query select all categories of logged-in-user, the second one all the categories not in logged-in-user preferences and the firs (external) one all the user wich do not have categories that logged-in-user not have.

E.g if logged-user has (motor, computer, sports) in his categories list

UserA has (motor, computer)

UserB has (motor, computer, bike)

UserA will be selectes while UserB wont

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SELECT * FROM users 
WHERE is_login = 1 
AND 
user_id IN (SELECT user_id FROM prod_list WHERE cat_id = {$id})