Imports System.Data.OleDb Public Class Form3 Dim con As New OleDbConnection Dim adp As New OleDbDataAdapter Dim ds As New DataSet Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load con.ConnectionString = "Provider=SQLOLEDB;Data Source=.;Integrated Security=SSPI;Initial Catalog=students" Dim selectcmd As New OleDbCommand selectcmd.CommandText = "select * from student" selectcmd.Connection = con adp.SelectCommand = selectcmd adp.Fill(ds, "student") End Sub Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click For Each txt As TextBox In Me.Controls.OfType(Of TextBox)() txt.Text = "" Next For Each combo As ComboBox In Me.Controls.OfType(Of ComboBox)() combo.Text = "" Next End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim insecmd As New OleDbCommand Dim Vs As String = TextBox1.Text & "','" & TextBox2.Text & "','" & ComboBox1.Text & "','" & ComboBox2.Text & "'," & TextBox3.Text & ",'" & ComboBox3.Text & ComboBox4.Text & ComboBox5.Text & "','" & TextBox4.Text & "','" & ComboBox6.Text & "','" & TextBox5.Text & "')" insecmd.CommandText = "insert into student values('" & Vs insecmd.Connection = con adp.InsertCommand = insecmd adp.Update(ds, "student") Me.Close() End Sub End Class

这是一个使用 OleDb 连接 SQL Server 数据库的 Windows 窗体应用程序的代码。在 Form3_Load 事件中，首先设置了数据库连接字符串，然后创建一个 OleDbCommand 对象并设置其 CommandText 和 Connection 属性，再创建一个 OleDbDataAdapter 对象并设置其 SelectCommand 属性，最后使用 Fill 方法将查询结果填充到 DataSet 对象中。

在 Button1_Click 事件中，首先创建一个 OleDbCommand 对象并设置其 CommandText 和 Connection 属性，然后将其设置为 OleDbDataAdapter 对象的 InsertCommand 属性。接着将要插入的数据拼接成一个字符串 Vs，将其作为 CommandText 的一部分，最后使用 Update 方法将数据插入到数据库中。在 Button2_Click 事件中，清空窗体中所有 TextBox 和 ComboBox 控件的文本。

相关问题

Imports System.Data.OleDb Public Class Form3 Dim con As New OleDbConnection Dim adp As New OleDbDataAdapter Dim ds As New DataSet Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load con.ConnectionString = "Provider=SQLOLEDB;Data Source=.;Integrated Security=SSPI;Initial Catalog=students" Dim selectcmd As New OleDbCommand selectcmd.CommandText = "select * from student" selectcmd.Connection = con adp.SelectCommand = selectcmd adp.Fill(ds, "Table") End Sub Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click For Each txt As TextBox In Me.Controls.OfType(Of TextBox)() txt.Text = "" Next For Each combo As ComboBox In Me.Controls.OfType(Of ComboBox)() combo.Text = "" Next End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim insecmd As New OleDbCommand Dim Vs As String = TextBox1.Text & "','" & TextBox2.Text & "','" & ComboBox1.Text & "','" & ComboBox2.Text & "'," & TextBox3.Text & ",'" & ComboBox3.Text & ComboBox4.Text & ComboBox5.Text & "','" & TextBox4.Text & "','" & ComboBox6.Text & "','" & TextBox5.Text & "')" insecmd.CommandText = "insert into student values('" & Vs insecmd.Connection = con adp.InsertCommand = insecmd adp.Update(ds) End Sub End Class这段代码有什么问题

这段代码有几个问题：

1. 连接字符串是针对 SQL Server 的，而不是 Access 数据库。应该使用 Access 数据库的连接字符串，例如：

   con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\MyDatabase.mdb"

2. 在插入数据时，字符串值应该使用参数化查询，而不是将值直接拼接到 SQL 语句中。这样可以避免 SQL 注入攻击，并且可以自动处理特殊字符的转义。应该改为类似下面的语句：

   insecmd.CommandText = "insert into student values(?, ?, ?, ?, ?, ?, ?, ?, ?)"
   insecmd.Parameters.AddWithValue("param1", TextBox1.Text)
   insecmd.Parameters.AddWithValue("param2", TextBox2.Text)
   '...

3. 在清空表单数据时，应该检查控件的类型是否为 TextBox 或 ComboBox，否则可能会出现异常。可以改为类似下面的语句：

   For Each ctrl As Control In Me.Controls
       If TypeOf ctrl Is TextBox Then
           DirectCast(ctrl, TextBox).Text = ""
       ElseIf TypeOf ctrl Is ComboBox Then
           DirectCast(ctrl, ComboBox).Text = ""
       End If
   Next

4. 在插入数据后应该更新 DataSet 中的数据，以便在下一次查询中可以看到新插入的记录。可以改为类似下面的语句：

   adp.Update(ds, "Table")

根据上述建议，可以将代码修改为：

Imports System.Data.OleDb

Public Class Form3
    Dim con As New OleDbConnection
    Dim adp As New OleDbDataAdapter
    Dim ds As New DataSet

    Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\MyDatabase.mdb"
        Dim selectcmd As New OleDbCommand
        selectcmd.CommandText = "select * from student"
        selectcmd.Connection = con
        adp.SelectCommand = selectcmd
        adp.Fill(ds, "Table")
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        For Each ctrl As Control In Me.Controls
            If TypeOf ctrl Is TextBox Then
                DirectCast(ctrl, TextBox).Text = ""
            ElseIf TypeOf ctrl Is ComboBox Then
                DirectCast(ctrl, ComboBox).Text = ""
            End If
        Next
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim insecmd As New OleDbCommand
        insecmd.CommandText = "insert into student values(?, ?, ?, ?, ?, ?, ?, ?, ?)"
        insecmd.Parameters.AddWithValue("param1", TextBox1.Text)
        insecmd.Parameters.AddWithValue("param2", TextBox2.Text)
        insecmd.Parameters.AddWithValue("param3", ComboBox1.Text)
        insecmd.Parameters.AddWithValue("param4", ComboBox2.Text)
        insecmd.Parameters.AddWithValue("param5", TextBox3.Text)
        insecmd.Parameters.AddWithValue("param6", ComboBox3.Text & ComboBox4.Text & ComboBox5.Text)
        insecmd.Parameters.AddWithValue("param7", TextBox4.Text)
        insecmd.Parameters.AddWithValue("param8", ComboBox6.Text)
        insecmd.Parameters.AddWithValue("param9", TextBox5.Text)
        insecmd.Connection = con
        adp.InsertCommand = insecmd
        adp.Update(ds, "Table")
    End Sub
End Class

Imports MySql.Data.MySqlClient Public Class Form1 Dim MysqlConn As MySqlConnection Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click MysqlConn = New MySqlConnection MysqlConn.ConnectionString = "server=localhost;useid=root;password=123456;database=testTJ_data" Try MysqlConn.Open() MessageBox.Show("Connection Successful") MysqlConn.Close() Catch ex As Exception MessageBox.Show(ex.Message) Finally MysqlConn.Dispose() End Try End Sub

这段代码是用来连接到 MySQL 数据库的。

首先，使用 `Imports MySql.Data.MySqlClient` 导入 MySQL 数据库所需的命名空间。

然后，在 `Form1` 类中定义一个 `MysqlConn` 变量，用于存储数据库连接对象。

接着，在 `Button1_Click` 事件处理程序中，创建新的 `MySqlConnection` 对象，并设置连接字符串为 `server=localhost;useid=root;password=123456;database=testTJ_data`。这个字符串中包含了连接到本地 MySQL 服务器，使用用户名为 root，密码为 123456，连接到名为 testTJ_data 的数据库。

然后，使用 `Try...Catch...Finally` 语句块来尝试连接到数据库。如果连接成功，会弹出一个消息框显示“Connection Successful”；如果连接失败，则会弹出一个消息框显示错误信息。最后，无论连接是否成功，都会释放 `MysqlConn` 对象。

需要注意的是，这段代码只是连接到数据库的代码，如果需要对数据库进行查询、插入、更新、删除等操作，还需要编写相应的 SQL 语句并执行。