这节课学习了链接数据库的增删改查，所有的变化都会同步到数据库中。跟着老师做中发现了几个问题
1.要运行的时候突然拦截了我的程序，说是有木马，给我吓一跳，我做的可是正经程序，后来查了一下看到了这个博客：HEUR/Malware.QVM03.Gen木马是360专有的误报
好的，那没事了。

2.老师多次强调把连接数据库的代码设置成全局变量，这样就不用每个函数里面都打一次了，但是当进行更新操作时，如果删除函数内部没有这行代码就只能进行一次修改，不能连续修改。相反，添加此代码即可多次更改。

老师只是给我们进行了简单的举例，很多地方还需要我们自己去优化。从今天开始要开始完成大作业，fighting！

以下是本次课讲解的基本增删改查的代码，功能性对来说并不齐全（例如只能修改姓名等）

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Login
{
    public partial class FormMain : Form
    {
        private object mrDavidDataSet;

        public FormMain()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        private void FormMain_Load(object sender, EventArgs e)
        {
            // TODO: 这行代码将数据加载到表“sCHOOLDataSet.Student”中。您可以根据需要移动或删除它。
            this.studentTableAdapter.Fill(this.sCHOOLDataSet.Student);

        }
        SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=SCHOOL;User ID=sa;Password=1234");
        private void insert_Click(object sender, EventArgs e)//增加
        {
            String StuID = textBox1.Text.Trim();
            String StuName = textBox2.Text.Trim();
            String StuSex = textBox3.Text.Trim();
            String StuAge = textBox4.Text.Trim();
            String StuSdept = textBox5.Text.Trim();
            try
            {
                con.Open();
                string insertStr = "INSERT INTO Student (Sno,Sname,Ssex,Sage,Sdept)" +
                                   "VALUES ('" + StuID + "','" + StuName + "','" + StuSex + "','" + StuAge + "'," + StuSdept +")";
                SqlCommand cmd = new SqlCommand(insertStr, con);
                cmd.ExecuteNonQuery();
            }
            catch
            {
                MessageBox.Show("输入数据违反要求!");
            }
            finally
            {
                con.Dispose();
            }
            this.studentTableAdapter.Fill(this.sCHOOLDataSet.Student);
        }

        private void delete_Click(object sender, EventArgs e)//删除
        {
            try
            {
                con.Open();
                string select_id = dataGridView1.SelectedRows[0].Cells[0].Value.ToString();//选择的当前行第一列的值，也就是ID
                string delete_by_id = "delete from Student where Sno=" + select_id;//sql删除语句
                SqlCommand cmd = new SqlCommand(delete_by_id, con);
                cmd.ExecuteNonQuery();
            }
            catch
            {
                MessageBox.Show("请正确选择行!");
            }
            finally
            {
                con.Dispose();
            }
            this.studentTableAdapter.Fill(this.sCHOOLDataSet.Student);
        }

        private void update_Click(object sender, EventArgs e)//修改
        {
            String StuID = textBox1.Text.Trim();
            String StuName = textBox2.Text.Trim();
            //SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=SCHOOL;User ID=sa;Password=1234");

            try
            {
                con.Open();
                string insertStr = "UPDATE Student SET Sname = '" + StuName + "' WHERe Sno = '" + StuID + "'";
                SqlCommand cmd = new SqlCommand(insertStr, con);
                cmd.ExecuteNonQuery();
            }
            catch
            {
                MessageBox.Show("输入数据违反要求!");
            }
            finally
            {
                con.Dispose();
            }
            this.studentTableAdapter.Fill(this.sCHOOLDataSet.Student);
        }

        private void select_Click(object sender, EventArgs e)//查询
        {
            String StuID = textBox1.Text.Trim();

            try
            {
                con.Open();
                String select_by_id = "select * from Student where Sno='" + StuID + "'";
                SqlCommand sqlCommand = new SqlCommand(select_by_id, con);
                SqlDataReader sqlDataReader = sqlCommand.ExecuteReader();
                BindingSource bindingSource = new BindingSource();
                bindingSource.DataSource = sqlDataReader;
                dataGridView1.DataSource = bindingSource;
            }
            catch
            {
                MessageBox.Show("查询语句有误，请认真检查SQL语句!");
            }
            finally
            {
                con.Close();
            }
        }
    }
}