我用的是三层结构，在数据访问层写了一个类
次类如下：
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace SQLtest.Classes
{
    class DB
    {
        public static string strConn = "DataSource=JC-MACHINE; DataBase=Student; User id=sa; PWD=jackylove";

        public void ExecuteNoneQuery(string strSQL)
        {
            SqlConnection myConn = new SqlConnection(strConn);
            SqlCommand myCmd = new SqlCommand(strSQL, myConn);

            try
            {
                myConn.Open();
                myCmd.ExecuteNonQuery();               
            }

            catch (SqlException se)
            {
                MessageBox.Show(se.Message, "錯誤信息：");
            }

            finally
            {
                myCmd.Dispose();
                myConn.Close();
            }

        }

        public SqlDataReader ExecuteReader(string strSQL)
        {
            SqlConnection myConn = new SqlConnection(strConn);
            SqlCommand myCmd = new SqlCommand(strSQL, myConn);

            try
            {
                myConn.Open();
                SqlDataReader myReader = myCmd.ExecuteReader();
                return myReader;
            }

            catch (SqlException se)
            {
                MessageBox.Show(se.Message, "錯誤信息：");
            }

            finally
            {
                myCmd.Dispose();
                myConn.Close();
            }

        }

        public DataSet GetDS(string strSQL)
        {
            SqlConnection myConn = new SqlConnection(strConn);
            SqlCommand myCmd = new SqlCommand(strSQL, myConn);

            try
            {
                myConn.Open();
                SqlDataAdapter myDa = new SqlDataAdapter(myCmd);
                DataSet myDs = new DataSet();
                myDa.Fill(myDs);
                return myDs;
            }

            catch (SqlException se)
            {
                MessageBox.Show(se.Message, "錯誤信息：");
            }

            finally
            {
                myCmd.Dispose();
                myConn.Close();
            }

        }

    }

   

}


就第一个方法编译可以通过，其他方法编译通不过。
且错误信息是：错误    2    “SQLtest.Classes.DB.GetDS(string)”: 并非所有的代码路径都返回值    D:\源程序文件\SQLtest\SQLtest\Classes\DB.cs    63    24    SQLtest

请问如何解决？

谢谢~！

顺便再帮我写一个返回一个结果的方法，和一个SQL事物的方法。
在下新手~！
多谢大家！！！！

public DataSet GetDS(string strSQL)
        {
            DataSet myDs = new DataSet();
            SqlConnection myConn = new SqlConnection(strConn);
            SqlCommand myCmd = new SqlCommand(strSQL, myConn);

            try
            {
                myConn.Open();
                SqlDataAdapter myDa = new SqlDataAdapter(myCmd);
                myDa.Fill(myDs);
            }

            catch (SqlException se)
            {
                MessageBox.Show(se.Message, "錯誤信息：");
            }

            finally
            {
                myCmd.Dispose();
                myConn.Close();
            }  
            return myDs;

        }