compare two tables

[twitch]

After trying for a couple of hours, I finally decided to give up and seek help. The gurus on this site always seem to come through.

Basically all I'm trying to do is look at two tables (each contains an idnum field) and list the numbers that are in table_2 AND in table_1.

I thought this would work:

$current = mysql_query("SELECT table_2.* FROM table_2
		LEFT JOIN table_1 ON table_2.idnum = table_1.idnum
		WHERE table_1.idnum IS NULL
		GROUP BY table_2.idnum");


while($row3 = mysql_fetch_array($current))
{
 echo $row3['idnum'];
  }

This just seems to output all the idnum in table_2

Any help would be much appreciated.

Thanks in advance,
Twitch

[twitch]

Never mind guys. I got it. It was simpler than I thought.

SELECT table_1.idnum, table_2.idnum ".
 "FROM table_1, table_2 ".
	"WHERE table_2.idnum = table_1.idnum