在设计页面里使用变量出现问题

Question

要实现的功能是根据dropdownlist的不用选项，调用不同的sql查询语句
出现错误为：selectcommand无法查询，提示错误如下：'<' 附近有语法错误。 
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。 异常详细信息: System.Data.SqlClient.SqlException: '<' 附近有语法错误。<%string sql;
          if (int.Parse( this.DropDownList1.SelectedValue) == 1)
          {
              sql = "select * from products";
          }
          else
              sql = "SELECT * FROM [products] WHERE ([typ_id] = @typ_id)";
            
             %>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:GoodsConnectionString %>"
            SelectCommand="<% =sql %>">
            <SelectParameters>
                <asp:ControlParameter ControlID="DropDownList1" Name="typ_id" PropertyName="SelectedValue"
                    Type="Int32" />
            </SelectParameters>
        </asp:SqlDataSource>

Answer 1

把<% %>换成 <script runat="server"></script>

Answer 2

可能还需要指定一下语言，vb.net好像是默认的

Answer 3

改进为以下还是出现同样的错误
<script runat="server">
            protected string sqltext()
            {
                string sql;
                if (int.Parse(this.DropDownList1.SelectedValue) == 1)
                {
                    sql = "select * from products";
                }
                else
                    sql = "SELECT * FROM [products] WHERE ([typ_id] = @typ_id)";
                return sql;
            }
         </script>
        
       
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:GoodsConnectionString %>"
            SelectCommand="<% =sqltext() %>">
            <SelectParameters>
                <asp:ControlParameter ControlID="DropDownList1" Name="typ_id" PropertyName="SelectedValue"
                    Type="Int32" />
            </SelectParameters>
        </asp:SqlDataSource>

Answer 4

SelectCommand="<% =sqltext() %>">
===
先把这里替换成实际的字符串测试一下