ผมสงสัยครับระหว่างการเขียน php เชื่่อมกับ sql ครับ ยังไงรบกวนๆ พี่ด้วยครับ

$arrayCou = Array();
	$sql_cou = "select id,courses_id,courses_name,credit from courses order by courses_id ASC";
	$rec_cou = mysql_query($sql_cou)or die("Error: $sql_cou <br /> File: ".__FILE__." Line: ".__LINE__);
	while($row_cou = mysql_fetch_assoc($rec_cou)){
		$arrayCou[$row_cou['id']] = $row_cou['courses_id'].'@'.$row_cou['courses_name'].'@'.$row_cou['credit'];
	}
	$sql = "select courses_id from major_curriculum_courses where major_curriculum_id='1' order by courses_id ASC";
	$rec = mysql_query($sql)or die("Error: $sql <br /> File: ".__FILE__." Line: ".__LINE__);
	while($row = mysql_fetch_assoc($rec)){
		echo $arrayCou[$row['courses_id']];
	}

	$sql = "select courses_id from major_curriculum_courses where major_curriculum_id='1' order by courses_id ASC";
	$rec = mysql_query($sql)or die("Error: $sql <br /> File: ".__FILE__." Line: ".__LINE__);
	while($row = mysql_fetch_assoc($rec)){
		$tmpID = $row['courses_id'];
		$sql_cou = "select id,courses_id,courses_name,credit from courses where courses_id='$tmpID'";
		$rec_cou = mysql_query($sql_cou)or die("Error: $sql_cou <br /> File: ".__FILE__." Line: ".__LINE__);
		echo  $row_cou['courses_id'].'@'.$row_cou['courses_name'].'@'.$row_cou['credit'];
	}