在 vb.net 中连接到 mysql

Question

我试图在 Visual Basic 2010 中从 VB.NET 连接 MySql。我想查询 db 只是为了获得一个返回，即单击按钮后对我的 proID 的响应。它成功显示连接已建立，但我似乎无法对其运行任何 sql 查询。可能出了什么问题？

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

假设按键事件中的 num 为 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

试试这个代码：

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）。

你想达到什么目标？如果您想从product 表中获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