MySQL connection failing "user#LAPTOP..." (using password: NO) - mysql

Question

I'm an absolute beginner in MySQL and trying to build a connection to my Visual Basic program. I use XAMPP and created a new user (admin) with a password. When I try to make the connection, it fails instead of using the right password.
I installed .NET Connector and ODBC Connector and imported the MySQL dll.
If you're able to help me, please answer as detailed as possible.
Private Sub btn_KI_Anzeigen_Click(sender As Object, e As EventArgs) Handles btn_KI_Anzeigen.Click
Dim connectionString As String = "server=localhost; database=notava; user id=****; password=****"
con.Open()
cmd.CommandText = "SELECT *, lehrer.name FROM klasse JOIN lehrer WHERE klasse.id_Klasse = " & id_Klasse & "AND WHERE klasse.id_tutor = lehrer.id_lehrer"
reader = cmd.ExecuteReader
lbl_KI_Klasseninfo.Text = "Klasse: " & cmb_KI_Jahrgang.SelectedItem & cmb_KI_Klasse.SelectedItem & vbCrLf &
vbCrLf & "Anzahl Schüler: " & reader("klasse.Anzahl_Schueler") & vbCrLf &
vbCrLf & "Tutor: " & reader("lehrer.name")
reader.Close()
con.Close()
End Sub
Error:
MySql.Data.MySqlClient.MySqlException: "Authentication to host '' for
user '' using method 'mysql_native_password' failed with message:
Access denied for user ''#'LAPTOP-D1CFSJ0F.speedport.ip' (using
password: NO)"
MySqlException: Access denied for user
''#'LAPTOP-D1CFSJ0F.speedport.ip' (using password: NO)

Answer 1

Keep your database object local so you can assure that they are closed and disposed. `Using...End Using blocks will do this for you even if there is an error.
Pass your connection string directly to the constructor of the connection.
Pass the sql statement and the connection directly to the constructor of the command.
As to your Select statement:
Don't use "*". You will get all the fields form both tables. It looks like you only need one field from each table. Don't retrieve unnecessary data.
A JOIN is done with an ON clause. If you did have more then one condition for the WHERE clause (not the case here) you would have a single WHERE and the additional conditions would be separated by AND.
You must call .Read on the reader to move to the first record. .Read advances the DataReader one record.
I used an Interpolated string for the label text. It saves all those ampersands and quotes also the Interpolated string assumes you want a string form the variables so you don't have to call .ToString explicitly. You can add hard returns by hitting Enter. VB adds the return for you again avoiding extra typing of ampersands and quotes.
Regarding the connection string. It looks like the database is on the same machine. My connection string looks like this server=localhost;user id=****;password=****;database=student where the **** would be replaced by your credentials. This URL has everything you ever wanted to know about connection strings. https://www.connectionstrings.com/mysql/
Private Sub Button4_Click(sender As Object, e As EventArgs) Handles Button4.Click
Dim sql = "SELECT klasse.Anzahl_Schueler, lehrer.name FROM klasse JOIN lehrer ON klasse.id_tutor = lehrer.id_lehrer WHERE klasse.id_Klasse = #idKlasse"
Using con As New MySqlConnection("server=localhost; database=notava; user id=****; password=****")
Using cmd As New MySqlCommand(sql, con)
cmd.Parameters.Add("#idKlasse", MySqlDbType.Int32).Value = id_Klasse
con.Open()
Using reader = cmd.ExecuteReader
reader.Read()
lbl_KI_Klasseninfo.Text = $"Klasse: {cmb_KI_Jahrgang.SelectedItem} {cmb_KI_Klasse.SelectedItem}
Anzahl Schüler: {reader("klasse.Anzahl_Schueler")}
Tutor: {reader("lehrer.name")}"
End Using
End Using
End Using
End Sub