ADO.NET数据访问(2) 查询数据

一：使用DataReader读取数据

 private void button1_Click(object sender, EventArgs e)        {            string s = "server=.;database=SampleDb;integrated security=true;";            SqlConnection conn = new SqlConnection(s);            SqlCommand cmd = new SqlCommand();            string sql = "select  * from  student";            cmd.CommandText = sql;            cmd.Connection = conn;            conn.Open();            SqlDataReader reader = cmd.ExecuteReader();            string id, name, gender, major;            int grade, cls;            object o;            while (reader.Read())            {                o = reader["id"];                id=(string) o;                name = (string)reader["name"];                gender = (string)reader["gender"];                major = (string)reader["major"];                grade = (int)reader["grade"];                cls = (int)reader["class"];                string temp=string.Format("{0}\t{1}\t{2}\t{3}\t{4}\t{5}\n",                    id, name, gender, major, grade, cls);                textBox1.AppendText(temp);            }            reader.Close();            conn.Close();        }

二：使用综合条件查询，grade和gender两个条件查询。

 private void button4_Click(object sender, EventArgs e)        {            textBox1.Text = "";            string s = "server=.;database=SampleDb;integrated security=true;";            SqlConnection conn = new SqlConnection(s);            SqlCommand cmd = new SqlCommand();            string sql = "select  * from  student ";            string where = " where 1=1 ";            if (textBox2.Text != "")             where = where + " and grade=" + textBox2.Text;            if (textBox3.Text  != "")                where = where + " and gender='" + textBox3.Text + "'";//字符串需加引号            sql = sql + where;            cmd.CommandText = sql;            cmd.Connection = conn;            conn.Open();            SqlDataReader reader = cmd.ExecuteReader();            string id, name, gender, major;            int grade, cls;            object o;            while (reader.Read())            {                o = reader["id"];                id = (string)o;                name = (string)reader["name"];                gender = (string)reader["gender"];                major = (string)reader["major"];                grade = (int)reader["grade"];                cls = (int)reader["class"];                              string temp = string.Format("{0}\t{1}\t{2}\t{3}\t{4}\t{5}\n",                   id, name, gender, major, grade, cls);                textBox1.AppendText(temp);            }            reader.Close();            conn.Close();

三：使用.DataGridView显示数据

显示或查询

 private void button1_Click(object sender, EventArgs e)        {            string s = "server=.;database=SampleDb;integrated security=true;";            SqlConnection conn = new SqlConnection();            conn.ConnectionString = s;             ds = new DataSet();             adapter = new SqlDataAdapter("select * from student",conn);            adapter.Fill(ds);            grid.DataSource = ds.Tables[0];        }

保存

 private void button2_Click(object sender, EventArgs e)        {            SqlCommandBuilder builder = new SqlCommandBuilder(adapter);            adapter.Update(ds);            MessageBox.Show("保存成功！");        }