donet framework4.X==windows窗体应用新建项目，通过System.Data.SqlClient连接sqlserver进行查询

 双击login按钮，注册事件，自动跳转到相关代码，程序运行的时候点击按钮就会自动执行对应代码

连接sqlserver数据库，查询数据 

不使用占位符

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

namespace WindowsFormsApp1sqlserver
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
//获取到刚才可视化界面画的图形中的内容，根据属性中设置名称来获取
            string _id = this.account.Text.Trim();
            string _name = this.password.Text;

//从sqlserver里查询数据
            SqlConnection conn= new SqlConnection("server=你的数据库IP地址;uid=sa;pwd=qwe20211114.;database=sqlserver2017_db");
            conn.Open();

            //sql server不能用user做表名
            string sql = $"select id,name from usertable where id='{_id}' and name='{_name}'";
            SqlCommand command= new SqlCommand(sql, conn);
           SqlDataReader reader= command.ExecuteReader();
            reader.Read();
            string id= reader["name"].ToString();
            MessageBox.Show(id);
            conn.Close();
            
        }
    }
}

使用占位符防止sql注入

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

namespace WindowsFormsApp1sqlserver
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string _id = this.account.Text.Trim();
            string _name = this.password.Text;

            SqlConnection conn= new SqlConnection("server=你的IP地址;uid=sa;pwd=qwe20211114.;database=sqlserver2017_db");
            conn.Open();

            //sql server不能用user做表名
            string sql = $"select id,name from usertable where [email protected] and [email protected]";
            SqlParameter[] parms = { 
            new SqlParameter("@userid",_id),
            new SqlParameter("@username",_name)
               }; 
            SqlCommand command= new SqlCommand(sql, conn);
            command.Parameters.AddRange(parms);
           SqlDataReader reader= command.ExecuteReader();
            reader.Read();
            string id= reader["name"].ToString();
            MessageBox.Show(id);
            conn.Close();
            
        }
    }
}