15小项目 连接数据库+读取信息

1.新建项目：

2.头文件：
using System;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Data;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            comboBox1.SelectedIndex = 0;// 默认选中第一项
            comboBox2.SelectedIndex = 0;
            //必须先创建表头
            listView1.Columns.Add("员工号", listView1.Width / 2 - 1, HorizontalAlignment.Left);
            listView1.Columns.Add("员工姓名", listView1.Width / 2 - 1, HorizontalAlignment.Left);
        }

        private void button1_Click(object sender, EventArgs e)
        {

            string connStr = "Data Source=DESKTOP-CHKF0KA;Initial Catalog=temp;Integrated Security=True";//使用windows连接
            //DESKTOP-CHKF0KA      连接的数据库服务器名
            //temp   数据库名字

            SqlConnection conn = new SqlConnection(connStr);

            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                //MessageBox.Show("数据库连接成功！");//winform中可以用
                Console.WriteLine("连接成功");//控制台用
            }

            string t1 = comboBox1.Text;//EmpNo
            string sql = String.Format("select * from works w join employee e on w.EmpNo = e.EmpNo " +
                "join company c on w.CmpNo = c.CmpNo " +
                "where e.EmpNo = '{0}'",t1);//EmpName = '{0}' and t1,

            SqlCommand cmd = new SqlCommand(sql, conn);
            listView1.Items.Clear();

            try
            {
                SqlDataReader re = cmd.ExecuteReader();//.ExecuteNonQuery();

                Console.WriteLine("修改成功");

                if (!re.HasRows)//判断是否为空
                {
                    comboBox1.Text = "不存在该员工";
                    return;
                }
                //re.Read();
                //textBox1.Text = re["EmpName"].ToString();

                this.listView1.BeginUpdate();   //数据更新，UI暂时挂起，直到EndUpdate绘制控件，可以有效避免闪烁并大大提高加载速度

                for (int i = 0; re.Read(); i++)   //添加10行数据
                {
                    ListViewItem lvi = new ListViewItem();//放入表中

                    lvi.Text = re["EmpNo"].ToString();
                    lvi.SubItems.Add(re["EmpName"].ToString());
                    lvi.SubItems.Add(re["EmpSex"].ToString());
                    lvi.SubItems.Add(re["EmpAge"].ToString());

                    this.listView1.Items.Add(lvi);

                    //listView1.Text += re["EmpNo"].ToString();

                }
              this.listView1.EndUpdate();  //结束数据处理，UI界面一次性绘制。

            }
            catch (SqlException ae)
            {
                Console.WriteLine("修改失败");
                Console.WriteLine(ae.Message);
                MessageBox.Show("error");
            }
            finally
            {
              conn.Close();//对数据库操作完成后，需要关闭数据库，释放内存
            }

      }