(记录下方便自己复习)
概念
简单地理解为用来连接数据库的类。
工作流程
①Connection对象用来连接数据库。
两种连接方式：Windows身份验证 / sqlserver验证
private void button1_Click(object sender, EventArgs e) ???????{ ???????????????try ???????????????{ ??????????????????????????????????????//string Str = "server=.;Initial catalog="db_PWMS";integrated security=SSPI";//windows身份验证 ???????????????????string Str = "server=.;database="db_PWMS";uid=sa;pwd=***";//Sqlserver验证 ???????????????????//声明Str存储连接数据库的字符串。 ???????????????????//server=.。 服务器名称=等于本地 。 ???????????????????//Initial catalog="db_PWMS" ??数据库名=db_PWMS。 ???????????????????SqlConnection conn= new SqlConnection(Str);//声明对象 ???????????????????conn.Open();//连接上 ???????????????????if (conn.State==ConnectionState.Open)//State属性判断打开与否 ???????????????????{ ???????????????????????richTextBox1.Text = "已经打开"; ???????????????????} ???????????????} ???????????????catch ???????????????{ ???????????????????MessageBox.Show("连接失败"); ???????????????} ???????}②command对象用来操作数据库。（三个重要的方法：ExecuteNonQuery(),ExecuteReader(),ExecuteScalar()）
⑴以update(改数据)为例,用到ExecuteNonQuery()方法
private void button2_Click(object sender, EventArgs e) ???????{ ???????????????SqlConnection conn =new SqlConnection("server=.;Initial catalog=db_PWMS;integrated security=SSPI"); ???????????????conn.Open();//老规矩，先连接 ???????????try ???????????{ ???????????????SqlCommand cmd = new SqlCommand();//实例操作项cmd ???????????????cmd.Connection = conn;//操作conn这个数据库 ???????????????cmd.CommandText = "update Table_1 set Prices =3333 where Origin =‘国产‘";//操作这样一句SQL语句 ???????????????cmd.CommandType = CommandType.Text;//书上这么写的，不知道干嘛的，以后知道了再说。去掉这句话也没事。 ???????????????cmd.ExecuteNonQuery();//command对象重要的三个方法之一，执行增删改查 ???????????????int i = Convert.ToInt32(cmd.ExecuteNonQuery()); ???????????????label2.Text = i + "条数据发生改动"; ???????????} ???????????catch (Exception ex){ MessageBox.Show(ex.Message); } ???????}点击事件（button2）
执行前数据库
执行后
⑵以各种姿势查数据ExecuteScalar()
此方法的聚合函数
| 说明 | |
| AVG() | 平均值 |
| count() | 有几条数据 |
| max() | 最大值 |
| min() | 最小值 |
| sum() | 和 |
以count（）和max（）为例
private void button3_Click(object sender, EventArgs e) ???????{
???????????conn = new SqlConnection("server=.;Initial catalog=db_PWMS;integrated security=SSPI");
conn.Open(); ???????????try ???????????{ string s1 = "select count (2) from Table_1";//表数量count()
string s2 = "select max (Prices) from Table_1";//Prices最大值max()
string s2 = "select max (Prices) from Table_1";//Prices最大值max()
SqlCommand cmd = new SqlCommand(s1,conn);
SqlCommand cmd1 = new SqlCommand(s2,conn);
SqlCommand cmd1 = new SqlCommand(s2,conn);
???????????????int i = Convert.ToInt32(cmd.ExecuteScalar());//对象转int类型 ???????????????int j = Convert.ToInt32(cmd1.ExecuteScalar()); ???????????????label2.Text = i+"条数据"; ???????????????label1.Text = "最贵的" + j; ???????????} ???????????catch (Exception ex){ MessageBox.Show(ex.Message); } ???????}ADO.NET基础学习
原文地址：https://www.cnblogs.com/zx3180/p/9112897.html