ADO.NET 数据查询和数据操作

    //数据查询 DT-PC\SQLEXPRESS
        public static DataTable MyQuery(string str)
        {
            SqlConnection conn = new SqlConnection("data source=.; database=LJC0125_web; Integrated Security=SSPI");
            conn.Open();
            SqlDataAdapter da = new SqlDataAdapter(str, conn);
            DataTable dt = new DataTable();
            da.Fill(dt);
            conn.Close();
            return dt;
        }
    //数据操作
        public static int MyExcute(string str)
        {
            SqlConnection conn = new SqlConnection("data source=.; database=LJC0125_web; Integrated Security=SSPI");
            conn.Open();
            //创建执行对象
            SqlCommand cmd = new SqlCommand(str, conn);
            //3.执行操作，返回受影响的行数
            int i = cmd.ExecuteNonQuery();
            //关闭连接
            conn.Close();
            //返回受影响行数
            return i;
        }

 //对表的操作
     private void Form3_Load(object sender, EventArgs e)
        {
            //在数据集中添加表
            DataTable tbl = new DataTable("user");
            ds.Tables.Add(tbl);

            //定义表的列
            DataColumn col = tbl.Columns.Add("id", typeof(Int32));
            col.AutoIncrement = true;
            col.AutoIncrementSeed = 0;
            col.AutoIncrementStep = 1;
            col.ReadOnly = true;

            tbl.Columns.Add("name", typeof(String));
            tbl.Columns.Add("birthday", typeof(DateTime));

            //定义id列为表的主键
            tbl.PrimaryKey = new DataColumn[] { tbl.Columns["id"] };

            //添加三行相同的数据
            for (int i = 0; i < 3; i++)
            {
                DataRow row = tbl.NewRow();
                row[1] = "llx";
                row[2] = DateTime.Now;
                tbl.Rows.Add(row);
            }

            //显示到DataGridView控件中
            dataGridView1.DataSource = ds.Tables["user"];


        }

        //添加一行
        private void button1_Click(object sender, EventArgs e)
        {
            DataTable tbl = ds.Tables["user"];
            DataRow row = tbl.NewRow();
            row[1] = textBox1.Text;
            row[2] = dateTimePicker1.Value;
            tbl.Rows.Add(row);
        }


        //删除最后一行
        private void button2_Click(object sender, EventArgs e)
        {
            DataTable tbl = ds.Tables["user"];
            if (tbl.Rows.Count > 0)
            {
                DataRow row = tbl.Rows[tbl.Rows.Count - 1];
                tbl.Rows.Remove(row);
            }
        }

        //修改行
        private void button3_Click(object sender, EventArgs e)
        {
            string s = "";

            string s = ""

            //查找特定行，进行修改
            DataTable tbl = ds.Tables["user"];
            DataRow row = tbl.Rows.Find(dataGridView1.CurrentRow.Cells[0].Value);

            if (row != null)
            {
                s += "未修改前为：" + row[1].ToString();
                if (textBox1.Text == "")
                    row[1] = DBNull.Value;
                else
                    row[1] = textBox1.Text;
                s += " 修改后为：" + row[1].ToString();
            }

            label1.Text = s;

            
        }