Permintaan pembaruan membuat bidang kosong di database

Bagaimana Anda memperbarui tabel di database Anda? Seharusnya seperti:(Saya akan mengambil kode saya untuk proyek lama yang saya lakukan)

Private Sub disconnect()
    conn.Close()
End Sub

Private Sub connect()
    conn.ConnectionString = connectionString
    conn.Open()
End Sub

Private Sub btnSaveEdit_Click(sender As Object, e As EventArgs) Handles btnSaveEdit.Click

connect()
Dim query as string
Dim command As New MySqlCommand

query = "Update `tblcandidates` set firstname = '" & txtEditFname.Text & "', lastname = '" & txtEditLName.Text & "', position='" & cboEditPosition.Text & "', fullname = '" & fullname & "' where recNum = '" & txtRec.Text & "'"



command.Connection = conn
command.CommandText = query

command.ExecuteNonQuery()

disconnect()
End Sub