CODE:

  Dim SQLflag As Boolean
    Dim db As New ADODB.Connection
    Dim rs As New ADODB.Recordset
    Dim strSEL As String
    Dim CON As String
Private Sub Connection_Click()
    'DB接続情報格納
    CON = "Provider = SQLOLEDB;Data Source = [IPアドレス];Initial Catalog=[データベース名];user id=hoge;password=hogehoge"
    
    db.Open (CON)
    SQLflag = True
    
    Connection.Enabled = False
    Connection_Close.Enabled = True
    GetData.Enabled = True
End Sub

Private Sub Connection_Close_Click()
    db.Close
    SQLflag = False
    Connection_Close.Enabled = False
    Connection.Enabled = True
    
End Sub

Private Sub GetData_Click()
    strSEL = "SELECT * from hogetable"
    Set rs = db.Execute(strSEL)
    Range("A1").Value = rs.Fields(0).Value
    Range("A2").Value = rs.Fields(1).Value
    
End Sub

Private Sub UserForm_Initialize()
    GetData.Enabled = False
    Connection.Enabled = True
    Connection_Close.Enabled = False
End Sub

Private Sub visible_Click()
    Dim flag As Boolean
    
    flag = Application.visible
    If flag = False Then
        Application.visible = True
    Else
        Application.visible = False
    End If
    
End Sub