$result = mysql_query("SELECT * FROM coupon WHERE Email_Address='$address'");

    if (mysql_num_rows($result)==0){
        echo "ADDING TO DATABASE: " . $address;
        if( FALSE === mysql_query("INSERT INTO coupon (Date_Issued, Email_Address, Coupon_Code, Coupon_Expiry) VALUES ('".date(Y-m-d)."', '$address', '$couponcode', LAST_DAY('".date(Y-m-d)."'))") ) echo mysql_error();

    }


/// ERROR: Column 'Coupon_Expiry' cannot be null