Question

I have never used JOINs or have worked with multiple table before.

This error is popping up.

Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in [pathway to this mysql_query line].

What am I doing wrong here?

Thank you.

$group_id= 4;

$result = mysql_query("SELECT table1.user_facebook_id AS user_facebook_id 
                       FROM table1 JOIN table2
                       ON table1.user_id = table2.user_id 
                       WHERE table2.group_id = $group_id");

$row = mysql_fetch_assoc($result);

Answer 1

You should test the value of $result to see if the query failed. If so, print the error for debugging purposes:

 $sql = "SELECT ...";
 $result = mysql_query($sql);
 if (!$result) {
     trigger_error(mysql_error());
 }

You may also want to try running the SQL query in the MySQL workbench to see if it works there.