c#经典编程实例（ado.net基本操作）

一：连接数据库之查询学生个数

查询学生个数代码如下：

   private void button1_Click(object sender, EventArgs e)        {            string s = "server=.;database=SampleDb;integrated security=true;";            SqlConnection conn = new SqlConnection();            conn.ConnectionString = s;            SqlCommand cmd = new SqlCommand();            string sql = "select  count(*) from  student";            cmd.CommandText = sql;            cmd.Connection = conn;            conn.Open();            object o = cmd.ExecuteScalar();            int n = (int)o;            conn.Close();            MessageBox.Show("学生共有" + n + "个学生");        }

功能如下：

举个例子 ：cmd.ExecuteNonQuery() 用于执行 update ，delete 等操作。可以返回更新了多少行，或者删除了多少行。 cmd.ExecuteScalar(); 可以用来返回像   select count（StudentName）from Students where Sex="男"这样的语句。返回一个结果值（这里是男生的人数）。

二：实现一个简单的登录页面

代码如下：

 private void button4_Click(object sender, EventArgs e)        {            string s = "server=.;database=SampleDb;integrated security=true;";            SqlConnection conn = new SqlConnection();            conn.ConnectionString = s;            SqlCommand cmd = new SqlCommand();            string sql = string.Format("select  count(*) from  student where Id='{0}'and name='{1}'",             textBox1.Text,textBox2.Text);            cmd.CommandText = sql;            cmd.Connection = conn;            conn.Open();            object o = cmd.ExecuteScalar();            int n = (int)o;            conn.Close();            if(n>0)            MessageBox.Show("登陆成功");        }

运行如下：

三：用sqldatareader实现读取学生功能

代码如下：

 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();        }

运行如下：

四：实现条件查询

用性别和年级

代码如下：

 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();        }

运行如下：

五：用datagirdview实现数据的查询和更删改查

代码如下；

显示的：

 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];        }

运行图：

及时保存的；

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

运行图：