如何编写用户登录时使用vb和sql server登录的代码？

Imports System.Data.SqlClient

Public Class LoginForm
    Dim conn As SqlConnection

    Private Sub LoginForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ' 连接数据库
        conn = New SqlConnection("Data Source=服务器地址;Initial Catalog=数据库名称;User ID=用户名;Password=密码")
        conn.Open()
    End Sub

    Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
        Dim username As String = txtUsername.Text
        Dim password As String = txtPassword.Text

        ' 执行查询
        Dim query As String = "SELECT * FROM 用户表 WHERE 用户名 = @username"
        Dim cmd As New SqlCommand(query, conn)
        cmd.Parameters.AddWithValue("@username", username)
        Dim reader As SqlDataReader = cmd.ExecuteReader()

        ' 验证登录
        If reader.Read() Then
            Dim dbPassword As String = reader("密码").ToString()
            If password = dbPassword Then
                MessageBox.Show("登录成功")
            Else
                MessageBox.Show("密码错误")
            End If
        Else
            MessageBox.Show("用户名不存在")
        End If

        reader.Close()
    End Sub

    Private Sub LoginForm_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
        ' 关闭数据库连接
        conn.Close()
    End Sub
End Class