ado.net考前複習

 1用於登錄的sql語句：
string sql = string.Format
("select count(*) from student where id='{0}'and name='{1}'", textBox1.Text, textBox2.Text);

 int n = (int)cmd.ExecuteScalar();
2.datagrideview顯示數據
string s = "server=.;database=SampleDb;integrated security=true;";
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = s;
            SqlCommand cmd = new SqlCommand();
            string sql = string.Format("select * from student");
            DataSet ds=new DataSet ();
            SqlDataAdapter  adapter=new SqlDataAdapter (sql,conn);
            adapter.Fill(ds);
            grid.DataSource=ds.Tables[0];
3.添加學生
string gender = radioButton1.Checked ? "男" : "女";
            string sql = string.Format("insert into student values('{0}','{1}','{2}','{3}',{4},{5})",
                textBox1.Text, textBox2.Text, gender,textBox3.Text, textBox4.Text, textBox5.Text);

4.刪除：
  string s1 = grid.CurrentRow.Cells[0].Value.ToString();
            string s = "server=.;database=SampleDb;integrated security=true;";
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = s;
            SqlCommand cmd = new SqlCommand();
            string sql = string.Format("delete from student where id='{0}'",s1);
            DataSet ds = new DataSet();
            SqlDataAdapter adapter = new SqlDataAdapter(sql, conn);
            adapter.Fill(ds);
            grid.DataSource = ds.Tables[0];


或  string sql = string.Format("delete from Course where Cno='{0}'", textBox1.Text);
5查詢：
 string sql = string.Format("select * from student where grade={0} and major like '%{1}%' and gender like '%{2}%'", textBox1.Text, textBox2.Text, textBox3.Text);

            grid.DataSource = "";
            string s = "server=.;database=SampleDb;integrated security=true;";
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = s;
           
            string sql = string.Format("select * from student where grade={0} and major like '%{1}%' and gender like '%{2}%'", textBox1.Text, textBox2.Text, textBox3.Text);
            DataSet ds = new DataSet();
            SqlDataAdapter adaper = new SqlDataAdapter(sql, conn);
            adaper.Fill(ds);

6.查詢學生個數

   string sql = "select count(*) from student";
  string sql = "select count(*) from student where gender='男'";
           int n =cmd.ExecuteScalar(sql);
            MessageBox.Show("共有" + n + "個男生");
            grid.DataSource = ds.Tables[0];
7.編輯


（1）string id = grid.CurrentRow.Cells[0].Value.ToString();
            EditStudentForm f = new EditStudentForm();
            f.id = id;
            DialogResult r = f.ShowDialog();
            if (r == DialogResult.OK)
                refereshData();

（2）
 public string id;           //學號，接收從列表窗體傳遞來的參數
        private void button1_Click(object sender, EventArgs e)
        {
            string g = r1.Checked ? "男" : "女";
            string sql = string.Format("update student set name='{0}',gender='{1}',major='{2}',grade={3},class={4} where id='{5}'",
                textBox2.Text,g, textBox4.Text, textBox5.Text, textBox6.Text, textBox1.Text);
            DbHelper.myExecute(sql);
            this.DialogResult = DialogResult.OK;
            this.Close();
        }

        private void EditStudentForm_Load(object sender, EventArgs e)
        {
            readStudent();
        }

        private void readStudent()
        {
            SqlConnection conn = DbHelper.createConnection();
            SqlCommand command = new SqlCommand();
            string sql = string.Format("select * from student where id ='{0}'", id);
            command.CommandText = sql;
            command.Connection = conn;
            conn.Open();
            SqlDataReader reader = command.ExecuteReader();           
            if (reader.Read())
            {
                textBox1.Text = reader["id"].ToString();                
                textBox2.Text = (string)reader["name"];
                textBox4.Text = (string)reader["major"];
                if (reader["gender"].ToString().Trim() == "男")
                    r1.Checked = true;
                else
                    r2.Checked = true;
                textBox5.Text = reader["grade"].ToString();
                textBox6.Text = reader["class"].ToString();                
            }
            reader.Close();
            conn.Close();

        }