如何在与c#中的本地数据库同步时避免远程数据库中的重复

Question

我尝试了代码，但失败了，因为当从本地数据库插入时，远程数据库中的行重复。

using System.Data.SQLite;
using System.Net.NetworkInformation;
using MySql.Data.MySqlClient;
namespace super
{
public partial class neworupload : Form
{
     SQLiteConnection con = new SQLiteConnection(@"connection string");
     MySqlConnection conn;
     String connstring;
     public neworupload()
     {
          InitializeComponent();
     }
     private void button1_Click(object sender, EventArgs e)
     {
          bool connection = NetworkInterface.GetIsNetworkAvailable();
          if (connection == true)
          {
               connstring = "SERVER=your ip;PORT=port;DATABASE=dbname;UID=userid;PASSWORD=password;SslMode = none;";
               try
               {
                    con.Open();
                    MessageBox.Show("Connection success");
                    String qu = "select * from users ";
                    SQLiteCommand cmd = new SQLiteCommand(qu, con);
                    SQLiteDataReader data = cmd.ExecuteReader();
                    while (data.Read())
                    {
                         String a = data["iduser"].ToString();
                         String b = data["name"].ToString();
                         String c = data["type"].ToString();
                         String d = data["email"].ToString();
                         String f = data["hash"].ToString();
                         Console.WriteLine(a);
                         Console.WriteLine(b);
                         Console.WriteLine(c);
                         Console.WriteLine(d);
                         Console.WriteLine(f);
                         conn = new MySqlConnection();
                         conn.ConnectionString = connstring;
                         conn.Open();
                         String qudemo = "select iduser from users";
                         Console.WriteLine("dddd" + qudemo);
                         String qu1 = "INSERT INTO users(iduser,name,type,email,hash) Values(@iduser,@name,@type,@email,@hash)";
                         MySqlCommand cmd1 = new MySqlCommand(qu1, conn);
                         cmd1.Parameters.AddWithValue("@iduser", a);
                         cmd1.Parameters.AddWithValue("@name", b);
                         cmd1.Parameters.AddWithValue("@type", c);
                         cmd1.Parameters.AddWithValue("@email", d);
                         cmd1.Parameters.AddWithValue("@hash", f);
                         cmd1.ExecuteNonQuery();
                         conn.Close();
                   }
                   con.Close();
               }
               catch (MySql.Data.MySqlClient.MySqlException ex)
               {
                   Console.WriteLine(ex);
               }
           }
           else
           {
                MessageBox.Show("Check connectivity and try again!");
           }
       }
   }
}

这里本地数据库包含7行，远程数据库包含5行。本地和远程数据库中的前5行是相同的。因此，当我们插入查询时，由于重复行而失败。实际上，额外的2行必须插入到远程数据库中。如何避免这个问题？

Answer 1

将上次保存的用户ID存储在本地数据库中，当您再次转到远程数据库同步数据时，将此where子句放入查询where RemoteDB.UserID > local.LastStoredUserID中。所以它只会获取新的记录...