MD5在sql查询中发布数据

i am trying to do the following, but is giving an error, what would be the correct way of writing the statement;

$sql="SELECT * FROM $tbl_name WHERE $db_usercol= '".$_POST['myusername']"' and $db_passcol= '"(md5($_POST['mypassword']))"'";
        $result=mysql_query($sql);

mysql_real_escape_string() is a good practice.

$sql = "SELECT * 
        FROM $tbl_name 
        WHERE $db_usercol= '" . mysql_real_escape_string($_POST['myusername']) . 
          "' AND $db_passcol= '" . (md5($_POST['mypassword'])) . "'";

also, you forgot the concatenation symbol, ..