Select with 2 tables

[stickman]

I dont know if this is possible, but I was wondering if there was a way to only select a user from table A if that user has at least one row in table B. Here is how I do it in PHP:

[code]
$query = "SELECT * FROM `table_a` ORDER BY `user`";
$result = mysql_query($query);
while($row = mysql_fetch_array($result)) {
    $query2 = "SELECT * FROM `table_b` WHERE `user_id` = '{$row['id']}'";
    $result2 = mysql_query($query2);
    if(mysql_num_rows($result2)==0) {continue;}
    echo $row['user'];
    echo "<br>";
}
[/code]

That will output every user that has at least one row in table B. I was wondering if there was any way to do that with 1 SELECT statement?

Thanks in advance for any help!!!

[stickman]

I figured it out. Here is my query for people who are asking the same question. I'm not sure if this is the proper way or not, but it works:

[code]SELECT * FROM `table_a` a, `table_b` b WHERE a.id = b.user_id GROUP BY a.user ORDER BY a.user[/code]

[fenway]

Well, first, proper JOIN syntax would be preferable; second, this doesn't satisfy your "at least" condition, since it will only retrieve those that match exactly.

[stickman]

The GROUP BY satisfies the at least. I dont need to return those rows or know how many rows there are, I just need to know if there is at least one row, but the user can have more. I'm not sure how to use the JOIN syntax.