Mysql update large table too much long time

[kkshansid]

I have two tables in database
table1 consisting of student data 4,00,000 records
table2 consisting of student examination center with roll nos range-800 records
I have to search roll no in range and then allocate center to it
i tried all methods but failed
first I tried to update by join it took infinite time to execute and resulted in browser hang
then I tried to go to student data through center allocation data and then executed update. loop has to execute 800 times but after 1:30 hours it gives time execution exceeds error.
Please help me to find a quickest method to do it
METHOD1-HANGS BROWSER

UPDATE STUDENTDATA INNER JOIN CENTER ON STUDENTDATA.SCH=CENTER.SCH SET EXAMCENTER = EXMCENTER
WHERE ROLLNO>=ROLLNO_FROM1 AND ROLLNO<=ROLLNO_TO1;

METHOD 2-ERROR AFTER 1:30 HOURS OF EXECUTION

?php 
//$myfile = fopen("cenfil17.txt", "w") or die("Unable to open file!");
include 'include/conn.php';
$sql = "update studentdata set examcenter=''" ;
$result = $conn->query($sql);
//SET  innodb_lock_wait_timeout = 5000; 
//ini_set('innodb_lock_wait_timeout', '5000');

		$pSCHOOL="1";$vSCHOOL="4";
		$sql = "select * from CENTER  order by SCHOOLNO2" ;
        $result = $conn->query($sql);
		ini_set('memory_limit', '-1');
		while($row = $result->fetch_assoc()) {
		$sql1 = "UPDATE studentdata  SET examcenter = '".$row["exmcenter"]."' WHERE SCH='".$row["SCH"]."' AND ( CAST(rollno AS UNSIGNED) BETWEEN " . $row["SERIAL_FROM"]." AND ". $row["SERIAL_TO"]." OR CAST(rollno AS UNSIGNED) BETWEEN " . $row["SERIAL_FROM1"]." AND ". $row["SERIAL_TO1"]. ")"  ;
	    ECHO $sql1."<BR/>";
		//EXIT;
        $result1 = $conn->query($sql1);	
			 
}
	
		
//fclose($myfile);
$conn->close();
?>

[Dormilich]

Please help me to find a quickest method to do it

use indexes

[kkshansid]

i tried index then
run method -1 that is bulk update method
but browser still browser hangs

[Dormilich]

then you need to let MySQL explain you the query.