源代码:

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SQLTest
{
    class Program
    {
        static void Main(string[] args)
        {
            //连接数据库
            string connection =
                "server=潘尚\\SQLEXPRESS;database=db_test;Trusted_Connection=true";
            SqlConnection sc = new SqlConnection(connection);
            sc.ConnectionString = connection;
            try
            {
                sc.Open();  //打开数据库连接
                Console.WriteLine("已经打开数据库连接!");
                string cmdtext = "DELETE FROM db_student WHERE student_name=@name";
                SqlCommand cmd = new SqlCommand(cmdtext, sc);
                cmd.Parameters.Add("@name", SqlDbType.VarChar).Value = "潘";
                int i = cmd.ExecuteNonQuery();
                if (i > 0) Console.WriteLine("删除记录成功!");
                //////添加记录的代码//////
            /*    SqlCommand cmd = new SqlCommand();//创建SqlCommand对象
                cmd.CommandType = CommandType.Text; //设置执行文本命令
                cmd.Connection = sc; //设置对象属性
                cmd.CommandText = 
                    "INSERT INTO db_student(student_name,student_age,student_address,student_grade)VALUES(@name,@age,@address,@grade)";
                //添加参数并为参数赋值
                cmd.Parameters.Add("@name", SqlDbType.VarChar, 10).Value = "潘";
                cmd.Parameters.Add("@age", SqlDbType.Int).Value = 19;
                cmd.Parameters.Add("@address", SqlDbType.VarChar).Value = "武汉";
                cmd.Parameters.Add("@grade", SqlDbType.Int).Value = 100;
                int i = cmd.ExecuteNonQuery(); //执行数据库添加记录命令
                if (i > 0) Console.WriteLine("添加记录成功"); //控制台输出添加记录
             * ////添加记录的代码///////*/
            }
            catch (Exception ex)
            {
                Console.WriteLine("打开数据库错误:{0}", ex.Message);
            }
            finally
            {
                sc.Close();
                Console.WriteLine("数据库连接已关闭!");
            }
            System.Console.ReadLine();
        }
    }
}

删除后的状态:

总结:注意cmdtext的正确性