嘗試並捕獲記錄數據

Question

我有代碼，如果有重複，那麼它會說「用戶名已存在」。但是，我們繼續在我的數據庫中記錄其他數據，如firstname,lastname和middlename（username除外）。如果一個數據有重複，我怎樣才能阻止它記錄其他值？

Try 
     Const SQLStatement As String = "START TRANSACTION; INSERT INTO people(Firstname, Middlename, Lastname) VALUES (@p0, @p1, @p2); 

INSERT account(uname, pass, type) VALUES(@p3, @p4,@p5); COMMIT;" 

       Using connection As New MySqlConnection() 
        connection.ConnectionString = ServerString 
        Dim command As New MySqlCommand(SQLStatement, connection) 
        command.Parameters.AddWithValue("@p0", firstname.Value) 
        command.Parameters.AddWithValue("@p1", middlename.Value) 
        command.Parameters.AddWithValue("@p2", lastname.Value) 
        command.Parameters.AddWithValue("@p3", username.Value) 
        command.Parameters.AddWithValue("@p4", password.Value) 
        command.Parameters.AddWithValue("@p5", type.Value) 
        connection.Open() 
        command.ExecuteNonQuery() 
       End Using 
       lblALabel.Text = "Successfully Registered!" 
       firstname.Value = "" 
       middlename.Value = "" 
       lastname.Value = "" 
       username.Value = "" 
       password.Value = "" 
      Catch ex As Exception 
       lblALabel.Text = "Username is taken" 
      End Try 

Answer 1

嘗試......
它會首先檢查「UserName」，如果不存在的話，你的數據將被插入。

Try 
     Const SQLStatement As String = "IF NOT EXISTS(SELECT * FROM ACCOUNT WHERE UNAME=@P3) 
     BEGIN 
      START TRANSACTION; 
      INSERT INTO people(Firstname, Middlename, Lastname) VALUES (@p0, @p1, @p2); 
      INSERT account(uname, pass, type) VALUES(@p3, @p4,@p5); 
      COMMIT; 
     END" 
     ....... 
     ....... 
    Catch ex As Exception 
     lblALabel.Text = "Username is taken" 
    End Try