子查询不适用于PHP

Question

我有桌子.我需要在我的查询中计算一些字段.这是我的查询:

select COUNT(q1) as 'result'
from (select DISTINCT id_qs as 'q1' FROM main where id_exam=40) as q2

这是查询完美的工作.但.当我把它放在PHP代码中:

   function HowManyQuestion($id)
   {
        mysql_connect($this->hostname,$this->username,$this->password) OR DIE("Can't connect");
        mysql_select_db($this->dbName) or die(mysql_error());
        $query = "select COUNT(q1) as 'result' from (select DISTINCT id_qs as 'q1' FROM main where id_exam=40) as q2;";
        $res = mysql_query($query) or die(mysql_error());
        $id=0;
        while ($row=mysql_fetch_array($res)) {
            $id=$row['result'];
            break;
        }
        return $id;

   }

结果我有错误:

您的SQL语法有错误; 检查与您的MySQL服务器版本相对应的手册,以便在第1行的'q2'附近使用正确的语法

那怎么解决？

Answer 1

实际上,您可以在不使用子查询的情况下简化查询,我认为这将删除错误.

SELECT COUNT(DISTINCT id_qs) totalCount
FROM main
WHERE id_exam = 40