ต้องการทำข้อสอบแบบสุ่มโดยแบ่งหมวดวิชาต่างๆอย่างละ 10 ข้อมารวมๆกันเป็นชุดเดียวครับ

<?
include "connect.php";
$sql="SELECT * FROM tb_test ORDER BY RAND() LIMIT 0,5
UNION ALL
SELECT * FROM test ORDER BY RAND() LIMIT 0,5";

$result=mysql_db_query($dbname,$sql);
while ($r=mysql_fetch_array($result)) { 	
	$id=$r[id];
	$question=$r[question];
	$choice1=$r[choice1];
	$choice2=$r[choice2];
	$choice3=$r[choice3];
	$choice4=$r[choice4];

	echo "<B>ข้อ $number. $question </B><BR>
	<INPUT TYPE='radio' NAME='select_$id' VALUE='1'> $choice1 <BR>
	<INPUT TYPE='radio' NAME='select_$id' VALUE='2'> $choice2 <BR>
	<INPUT TYPE='radio' NAME='select_$id' VALUE='3'> $choice3 <BR>
	<INPUT TYPE='radio' NAME='select_$id' VALUE='4'> $choice4 
	<INPUT TYPE='hidden' NAME='total_question[]' VALUE='$id'>
	<HR>	";
	$number++;
} 
mysql_close();
?>

 SELECT 'TB1' as tb1 , t1.title, t1.title_detail,t1.id,t1.dateup,t1.timeup FROM  tb_article t1 
UNION
  SELECT 'TB2' as tb2 , t2.title, t2.title_detail,t2.id,t2.dateup,t2.timeup FROM tb_journal t2