$sql = "UPDATE `$db_name`.`$tbl_name` SET `u_code` = '$u_code' WHERE `$tbl_name`.`email` = `$mail`;";
        $result=mysql_query($sql);

Whenever an email id (eg: mailme@gmail.com) is entered and the query is run then error occurs (No such e-mail exists in the database , Although it is present) but after some experiments it is found that instead of entering the email-id (eg: mailme@gmail.com) the word "email" is entered and the query is run...it works..but at the same time disturbs whole column {u_code} by changing the value to $u_code for all the database present.

Yani sorun MySQL sorgu gibi görünüyor .... ama ben bunu anlamaya olabilir.

Yardımın için teşekkürler! :)