从数据库中提取数据 ，计数（ count() ）但就是产生如下错误??急！！

[zl_xue]

各位大虾，小弟从数据库中提取数据 ，计数（ count() ）。但就是产生如下错误，怎么解决？谢先！！
代码如下：
<%
String Q_id="1";
String Q_num="1";
String sql2="select A_num,count(A_num) as counta from answered where Q_id='"+Q_id+"' and Q_num='"+Q_num+"'group by A_num";
ResultSet rs=db.executeQuery(sql2);
int count=0;
int counta=0;
while(rs.next()){
counta=rs.getInt("counta");//不加这行 ，没问题！！
count=rs.getInt("count");//不加这行 ，也没问题！！
int A_num=rs.getInt("A_num");
%>
错误如下：
javax.servlet.ServletException: Column not found
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:471)
at org.apache.jsp.a$jsp._jspService(a$jsp.java:124)

<%=A_num%>
<%=count%>
<%=counta%>
<%
}
rs.close();
%>

[zl_xue]

对不起，我把错误加错地方了。正确如下
代码如下：
<%
String Q_id="1";
String Q_num="1";
String sql2="select A_num,count(A_num) as counta from answered where Q_id='"+Q_id+"' and Q_num='"+Q_num+"'group by A_num";
ResultSet rs=db.executeQuery(sql2);
int count=0;
int counta=0;
while(rs.next()){
counta=rs.getInt("counta");//不加这行 ，没问题！！
count=rs.getInt("count");//不加这行 ，也没问题！！
int A_num=rs.getInt("A_num");
%>
<%=A_num%>
<%=count%>
<%=counta%>
<%
}
rs.close();
%>

错误如下：
javax.servlet.ServletException: Column not found
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:471)
at org.apache.jsp.a$jsp._jspService(a$jsp.java:124)

[Andrawu]

<%
String Q_id="1";
String Q_num="1";
String sql2="select A_num,count(A_num) as counta from answered where Q_id='"+Q_id+"' and Q_num='"+Q_num+"'group by A_num";
ResultSet rs=db.executeQuery(sql2);
int A_num=0;
int counta=0;
while(rs.next()){
A_num=rs.getInt("A_num");
counta=rs.getInt("counta");
%>
<%=A_num%>
<%=counta%>
<%
}
rs.close();
%>

[zl_xue]

谢先 但错误依旧，麻烦在帮忙想想！！万分感谢

[Jeff]

数据库有这列吗？或者列名大小写的问题

[zl_xue]

有，我输出String sql2 可以的。就是以复制给变量，就出问题！好急阿
帮帮忙！！谢谢

[advanced]

String sql2="select A_num,count(A_num) as 'counta' from answered where Q_id='"+Q_id+"' and Q_num='"+Q_num+"'group by A_num";

[利而不害]

A_num=rs.getInt(1);
counta=rs.getInt(2);

[zl_xue]

hazeline(砸死我) ：
对不起 ，麻烦你写的详细点，我看不懂。1、2是什么？

[zl_xue]

又出了新问题
错误如下：
javax.servlet.ServletException: [Microsoft][ODBC SQL Server Driver]无效的描述符索引
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:471)
at org.apache.jsp.a$jsp._jspService(a$jsp.java:125)
......

[bookbobby]

count(A_num) 是不能和别的列一起去出来的

如果需要取count(A_num) 列，必须单独用一个sql语句。

因为count(A_num) 只有一条纪录，而其他的列都可能是多条纪录

[zl_xue]

bookbobby(书呆)
谢了
给分