以下是一个简单的示例，演示如何比较数据库中的值与文本框中的值。

Imports System.Data.SqlClient

Public Class Form1

    Dim connString As String = "Data Source=YourServer;Initial Catalog=YourDatabase;Integrated Security=True"
    Dim conn As SqlConnection

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        conn = New SqlConnection(connString)
        conn.Open()
    End Sub

    Private Sub btnCompare_Click(sender As Object, e As EventArgs) Handles btnCompare.Click
        Dim query As String = "SELECT * FROM YourTable WHERE ColumnName = @Value"
        Dim cmd As SqlCommand = New SqlCommand(query, conn)
        cmd.Parameters.AddWithValue("@Value", txtValue.Text)

        Dim reader As SqlDataReader = cmd.ExecuteReader()
        If reader.HasRows Then
            MessageBox.Show("值存在于数据库中。")
        Else
            MessageBox.Show("值不存在于数据库中。")
        End If

        reader.Close()
    End Sub

    Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
        conn.Close()
    End Sub

End Class

请注意，您需要将YourServer替换为您的SQL Server实例名称，YourDatabase替换为您的数据库名称，YourTable替换为您要比较值的表的名称，ColumnName替换为要比较的列的名称。

此示例假设您已经在窗体上放置了一个名为txtValue的文本框和一个名为btnCompare的按钮。当用户点击btnCompare按钮时，它将执行查询并比较数据库中的值与文本框中输入的值。根据比较结果，将显示相应的消息框。