Question

How do i make a mysql query for more tables to check at once?
i mean, something like:

$sql = mysql_query("SELECT username FROM table1, table2, table3 WHERE username = '$username'");
$numer = mysql_num_rows($sql);
echo "You have ".$number;

can you do like this?

What i want to do is to show a user all his posts from the whole site..

Answer 1

In the query you provided, its using a full outer-join.
Use union selects instead.

SELECT username FROM table1 WHERE username = '$username'
UNION SELECT username FROM table2 WHERE username = '$username'
UNION SELECT username FROM table3 WHERE username = '$username'