简单的 VB 语法显示数据库中的一些值

Question

我对 Visual Basic 非常陌生（使用 Visual Studio 2010）。我只是做一些测试来连接到 mysql 数据库。

一旦我进行了 sql 查询，我不知道如何调用这些值。

我该如何处理这个问题，即在表单上的标签上显示值？

代码：

Imports MySql.Data.MySqlClient
Public Class Form1

    Dim ServerString As String = "Server = localhost; User Id = root; database = CALIBRA"
    Dim SQLConnection As MySqlConnection = New MySqlConnection

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        SQLConnection.ConnectionString = ServerString

        Try
            If SQLConnection.State = ConnectionState.Closed Then
                SQLConnection.Open()
                MsgBox("Successfully connected to MySQL database.")
            Else
                SQLConnection.Close()
                MsgBox("Connection is closed.")
            End If
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub

    Public Sub calibra_query(ByRef SQLStatement As String)
        Dim cmd As MySqlCommand = New MySqlCommand

        With cmd
            .CommandText = SQLStatement
            .CommandType = CommandType.Text
            .Connection = SQLConnection
            .ExecuteNonQuery()
        End With

        SQLConnection.Close()
        MsgBox("Records Successfully Retrieved")
        SQLConnection.Dispose()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim SQLStatement As String = "SELECT Auto1, Auto2, TotalWeight FROM txticket WHERE TicketCode = '12210'"
        calibra_query(SQLStatement)

        Dim Automobile1, Automobile2, TotalWgt As Long

    SOMETHING MISSING HERE
    SOMETHING MISSING HERE

    Label2.Text = Automobile1.ToString()
    Label2.Text = Automobile2.ToString()
    Label2.Text = TotalWgt.ToString()

    End Sub
End Class

我应该在“这里缺少什么”中输入什么？非常感谢。

Answer 1

您将需要一个数据读取器来读取 sql 查询返回的内容。您的 Sub calibra_query 正在执行非读取器，它不会执行您需要的操作。您只想将executeNonReader 用于不需要结果的事情。 （例如，像 Update 语句）

您想要更像这样的东西：

 Dim cmd As MySqlCommand = New MySqlCommand

With cmd
    .CommandText = SQLStatement
    .CommandType = CommandType.Text
    .Connection = SQLConnection
End With

  Dim myReader as MySqlDataReader = myCommand.ExecuteReader

  If myReader.Read Then
     TextBox1.Text = myReader.GetString(0)
     TextBox2.Text = myReader.Getstring(1)
     TextBox3.Text = myReader.GetInt32(2)
  End If

  myReader.Close()
  SQLConnection.Close()
  MsgBox("Records Successfully Retrieved")
  SQLConnection.Dispose()

我假设查询中 3 个字段的类型，然后将其输出到文本框以便为您提供想法。这还假设您最终只会得到一条记录。

（编辑：修复格式）