Question

我试图在Visual Basic 2010中从VB.NET连接MySql。我想查询数据库只是为了得到一个返回是我的proID响应一旦我点击按钮。它成功显示连接已建立但我似乎无法运行任何SQL查询。什么可能是错的？

这是我从即时窗口得到的错误：

A first chance exception of type 'System.InvalidOperationException' occurred in MySql.Data.dll

让我们假设来自keypress事件的num是1001。

Public Class Form1
    Private connStr As String = "server=localhost;" & _
                "user id=root;Password=1234561;" & _
                "database = test"
    Dim num As Integer


Private Sub TextBox1_keypress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
    Dim str As String
    If e.KeyChar = Microsoft.VisualBasic.ChrW(Keys.Enter) Then
        str = TextBox1.Text
        Dim splitVals As String() = str.Split(" ")
        num = splitVals(1)
    End If
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim query As String = "SELECT * FROM products"
    Dim con As New MySqlConnection(connStr)
    Dim cmd As New MySqlCommand(query)
    Try
        con.Open()
        MessageBox.Show("Database Connected")
        cmd.ExecuteNonQuery()
        cmd.Connection.Close()

        con.Close()
    Catch ex As Exception
        Console.WriteLine(ex.Message)
    End Try
End Sub

End Class

Answer 1

试用此代码：

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim query As String = "SELECT * FROM products"
    Dim con As New MySqlConnection(connStr)
    Dim da as New MySqlDataAdapter() 
    Dim ds as New DataSet
    Try
        con.Open()
        MessageBox.Show("Database Connected")
        da=New MySqlDataAdapter(query,con)
        da.fill(ds,"products") 
        DataGridView1.DataSource=ds.Tables("products")
        con.Close()
    Catch ex As Exception
        Console.WriteLine(ex.Message)
    End Try
End Sub

Answer 2

ExecuteNonQuery 用于不返回任何数据的SQL语句（例如，INSERT，UPDATE，DELETE）。

你想要达到什么目的？如果您想从product表中提取所有记录并将其显示在datagrid上，请尝试以下操作：

Using xConn as New MySqlConnection(connStr)
    Using xComm as new MySQLCommand()
        xComm.Connection = xConn
        xComm.CommandText = "SELECT * FROM products"
        Using xAdapter as new MySQLDAtaAdapter(xComm)
            Dim ds as new Dataset
            xConn.Open()
            xAdapter.Fill(ds)
            datagridview1.datasource = ds.tables(0)
        End Using
    End Using
End Using

更新1

Dim xPrice as Integer = 0
Using xConn as New MySqlConnection(connStr)
    Using xComm as new MySQLCommand()
        xComm.Connection = xConn
        xComm.CommandText = "SELECT ProductPrice FROM products WHERE proID = @xID"
            xComm.Parameters.AddWithValue("xID", "Value Here")
            xConn.Open()
            xPrice = CInt(xComm.ExecuteScalar())
            xConn.Close
    End Using
End Using

Msgbox xPrice

在vb.net中连接到mysql

2 个答案: