带参数的sql语句

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

namespace 带参数的sql语句
{
class Program
{
static void Main(string[] args)
{
string constr = “Server=localhost;Database=user;user=root;password=liuyang;”;
while (true)
{
Console.WriteLine(“请输入名称：”);
string u = Console.ReadLine();
Console.WriteLine(“请输入密码：”);
string p = Console.ReadLine();
using (SqlConnection conn = new SqlConnection(constr))
{

                //带参数的sql语句 @后代表参数名
                string sql = "select id from users where username=@username and password=@password";
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    conn.Open();

                    //声明变量，与sql语句中的参数绑定
                    //SqlParameter username = new SqlParameter("@username", System.Data.SqlDbType.VarChar, 50) { Value = u };
                    //SqlParameter password = new SqlParameter("@password", System.Data.SqlDbType.VarChar, 50) { Value = p };

                    //将变量添加到SqlCommand变量中
                    //cmd.Parameters.Add(username);
                    //cmd.Parameters.Add(password);

                    SqlParameter[] sq = new SqlParameter[] { new SqlParameter("@username", System.Data.SqlDbType.VarChar, 50) { Value = u }, new SqlParameter("@password", System.Data.SqlDbType.VarChar, 50) { Value = p } };

                    cmd.Parameters.AddRange(sq);
                    if (cmd.ExecuteScalar() != null)
                    {

                        //查询一个数据，使用cmd.ExecuteScalar()
                        int id = (int)cmd.ExecuteScalar();
                        Console.WriteLine(id);
                    }

                }
            }
        }
    }
}

}