php's mysqli_multi_query not working - php

Question

I've been trying to execute a multiple query, so I've searched for a better approach on how to do this and I've read this mysqli_multi_query in php.
I tried it on my own to see the results, but it keeps on giving me error. Here's the code:
$studid = $_GET['stud_id'];
$classcode = $_GET['class'];
$conn = new MySQLi($host, $username, $password, $dbname) or die('Can not connect to database');
$sql = "SELECT * FROM tbl_students WHERE stud_id = '".$studid."'";
$sql.= "SELECT * FROM tbl_classes WHERE class_code = '".$classcode."'";
if (mysqli_multi_query($conn, $sql)) {
do {
/* store first result set */
if ($result = mysqli_store_result($conn)) {
while ($row = mysqli_fetch_row($result)) {
$studname = $row[3].", ".$row[1];
}
mysqli_free_result($result);
}
/* print divider */
if (mysqli_more_results($conn)) {
printf("-----------------\n");
$studname = $row['fname'];
}
} while (mysqli_more_results($conn));
}else{ echo "error";}
$conn->close();
With the code above, it will just print error from the else statement I set. I also tried changing the second query to $sql .= "SELECT * FROM tbl_classes WHERE class_code = '".$classcode."'"; and also tried putting semicolon after the first query to tell the SQL that I'm done with the first query since I'm putting 2 strings together, but still no luck.

Answer 1

try this
$studid = $_GET['stud_id'];
$classcode = $_GET['class'];
$conn = new MySQLi($host, $username, $password, $dbname) or die('Can not connect to database');
$sql = "SELECT * FROM tbl_students WHERE stud_id = '$studid';";
$sql.= "SELECT * FROM tbl_classes WHERE class_code = '$classcode'";
if ($conn->multi_query($sql)) {
do {
/* store first result set */
if ($result = mysqli_store_result($conn)) {
while ($row = mysqli_fetch_row($result)) {
$studname = $row[3].", ".$row[1];
}
mysqli_free_result($result);
}
/* print divider */
if (mysqli_more_results($conn)) {
printf("-----------------\n");
$studname = $row['fname'];
}
} while (mysqli_more_results($conn));
}else{ echo "error";}
$conn->close();

Answer 2

Make one query instead of two :
"SELECT ts.*, tc.*
FROM tbl_students as ts, tbl_classes as tc
WHERE ts.stud_id = '$studid'
AND tc.class_code = '$classcode'"
Note : If you get redundant data then use group by.