C#连接SQL的增删改查

using System;
using System.Data.SqlClient;
using System.Data;

namespace Test
{
    class SQLHelper
    {
        //定义数据库连接实例
        private static SqlConnection con = CreateCon();

        //创建数据库连接静态方法
        public static SqlConnection CreateCon()
        {
            return new SqlConnection("server=127.0.0.1;database=test;uid=sa;pwd=123456");
        }

        /// <summary>
        /// 获取数据集
        /// </summary>
        /// <param name="sequal">数据库语句</param>
        /// <param name="tableName">数据表名称</param>
        /// <returns>返回数据集</returns>
        public static DataSet ExecuteDataSet(string sequal, string tableName)
        { 
            DataSet ds = new DataSet();
            try
            {
                //打开数据库连接
                con.Open();
                //创建数据库适配器连接
                SqlDataAdapter sda = new SqlDataAdapter(sequal, con);
                //填充数据集
                sda.Fill(ds, tableName);
                //返回数据集
                return ds;
            }catch(Exception ex)
            {
                throw new Exception(ex.Message);
            }
            finally
            {
                con.Close();
            }
        }

        /// <summary>
        /// 执行数据库命令并返回影响条数
        /// </summary>
        /// <param name="sequal">数据库语句</param>
        /// <returns>返回影响条数</returns>
        public static int ExecuteNonQuery(string sequal)
        {
            try
            {
                con.Open();
                //创建数据库操作命令
                SqlCommand cmd = new SqlCommand(sequal, con);
                //返回执行数据库影响条数
                return cmd.ExecuteNonQuery();
            }
            catch (Exception ex1)
            {
                throw new Exception(ex1.Message);
            }
            finally
            {
                con.Close();
            }
        }
    }
}
调用方法：
            //绑定winfrom中的表格(DataGridView)
            DataSet ds = SQLHelper.ExecuteDataSet("select * from t1", "tableName");
            DataGridView1.DataSource = ds.Tables["tableName"];

            //添加数据
            string str0 = "添加";
            int count0 = SQLHelper.ExecuteNonQuery("insert into t1 (name) values ('" + str0 + "')");
            if (count0 > 0)
                MessageBox.Show("添加了" + count0 + "条数据!");
            //修改数据
            string str1 = "修改";
            int count1 = SQLHelper.ExecuteNonQuery("update t1 set name = '" + str1 + "'");
            if (count0 > 0)
                MessageBox.Show("修改了" + count1 + "条数据!");
            //删除数据
            int count2 = SQLHelper.ExecuteNonQuery("delete from t1");
            if (count2 > 0)
                MessageBox.Show("删除了" + count2 + "条数据!");