C# 登录界面从数据库取用户名密码匹配结束后进入登录界面

private void button9_Click(object sender, EventArgs e)

        {

            string constr = "server=XB-20160802BVHL;database=Level_2;uid=sa;pwd=wly561561";//连接字符串里包含了数据库信息

            SqlConnection cnn = new SqlConnection(constr);//创建数据库连接

            cnn.Open();//打开连接

           

            string sql = "select * from 用户信息 where 用户名='" + textBox1.Text + "' and 密码 ='" + textBox2.Text + "'";

            SqlCommand cmd = new SqlCommand();  //SqlCommand表示对数据库要执行的操作命令。

            SqlDataAdapter da = new SqlDataAdapter(sql,cnn);

            DataSet ds = new DataSet();

            da.Fill(ds,"用户信息");

            DataTable dt = new DataTable();

            if (ds.Tables[0].Rows.Count > 0)

            {

                this.Hide();

            }

            else 

            {

                MessageBox.Show("用户名或者密码错误！");

                textBox1.Text = "";

                textBox2.Text = "";

            }

        }       

 

        private void button10_Click(object sender, EventArgs e)

        {

            Application.Exit();

        }