Passing value from php to?

I am going to select a list of items from a table, and pass it using json-framework.

Example, I want to select frien开发者_运维知识库ds from my "shirts" table, from "players_shirts" table

pid    |    sid
================
 1     |     2
 2     |     3
 1     |     5

Lets say, I get 30++ result (rows).

I assume (not yet tested this code), in php, I assign it by:

$array;
$count = 0;
while($r = mysql_fetch_assoc($exe){
    $array[$count] = $r['sid'];
    // EDIT START: I forgot to add counter
    $count++;
    // EDIT END
}

echo json_encode($array)

Is this method efficient/good enough?

I am new to php/database/manipulating data from database.

There is no need to specify an array keys in your case, so your code could be rewritten as:

$array = array();
while($r = mysql_fetch_assoc($exe){
    $array[] = $r['sid'];
    // or you may use array_push($array, $r['sid']); instead of the line above.
}