How to check whether SELECT EXISTS returns a value or not?

Question

I am trying to quickly determine if a user_ID is the owner of a \'goal\'. I believe my SQL query is good, but I\'m trying to find a nice way of checking the result!

Answer 1

Don't bother with EXISTS. The in-line exists will always give one row containing "true" or "false".

You're looking for either "zero rows" or "at least one row" so change the query to something like this and then check how many rows are returned

SELECT 1 FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id' LIMIT 1

Answer 2

Counting how many rows match the criteria should be easier:

$sql = SELECT COUNT(*) FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id'
$query = mysql_query($sql);
$result = mysql_fetch_row($query);

return $result[0] >= 1;

Answer 3

what about this:

$query = "SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')";

return  mysql_query($query) ? false : true;

Answer 4

This way is probably faster.

$query = "SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')";

if(mysql_num_rows(mysqli_query($query)) < 1) {
   // Nothing found!
}

Answer 5

SELECT EXISTS always returns a row! The following code uses the fastest MySql query(according to this answer: https://stackoverflow.com/a/10688065/3710053) and gives in PHP the correct result:

$link = mysqli_connect($DB_SERV, $DB_USER, $DB_PASS, $DB_NAME);
$query = "SELECT EXISTS (SELECT * FROM goals 
                      WHERE goal_ID='$obj_id' 
                        AND user_ID='$user_id' 
                      LIMIT 1) 
      as `row_exists`";

if(mysqli_fetch_assoc(mysqli_query($link,$query))['row_exists'] ===0) {
   // Nothing found!
}

Answer 6

mysql_result(mysql_query("SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')"),0);