Avoid Duplicate record across columns - c#-to-vb.net

Question

I Have a code that will determine if a data is already existing. The problem is, it is still adding even already exists.
Already tried some code that will add and not add if data exists
If txtHostname.Text = "" Then
MsgBox("Please fill-up all fields!", MsgBoxStyle.Exclamation, "Inventory!")
Else
Dim theQuery As String = "SELECT * FROM Asset WHERE Monitor1=#Monitor1 AND Monitor2=#Monitor2"
Dim cmd1 As OleDbCommand = New OleDbCommand(theQuery, con)
cmd1.Parameters.AddWithValue("#Monitor1", txtMonitor1.Text)
cmd1.Parameters.AddWithValue("#Monitor2", txtMonitor2.Text)
Using reader As OleDbDataReader = cmd1.ExecuteReader()
If reader.HasRows Then
' User already exists
MsgBox("User Already Exist!", MsgBoxStyle.Exclamation, "Add New User!")
Else
' User does not exist, add them
Dim cmd As OleDbCommand = New OleDbCommand("Insert into Asset ([Monitor1],[Monitor2]) values ('" + txtMonitor1.Text + "','" + txtMonitor2.Text + "')", con2)
cmd.ExecuteNonQuery()
MsgBox("Records Successfully Added!", MsgBoxStyle.Information, "Add New Customer!")
txtMonitor1.Text = ""
txtMonitor2.Text = ""
End If
End Using
con.Close()
End If
It should be, when I search 1 data in column1 it should detect if data is already exists in column1 and column2. Not just in column1.

Answer 1

Well, if you want to search and return the result about whether Fields exist or not , you should not use OledbReader, also I did notice that reader doesn't Read (Even if it is not even correct to use it in this scenario). You could rather use ExecuteScalar and see if Fields exist or not (>0 or <0).
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim CMDText As String = ("SELECT COUNT(*) FROM Asset WHERE Monitor1=#Monitor1 AND Monitor2=#Monitor2")
Dim Found As Integer
If String.IsNullOrEmpty(txtHostname.Text) Then
MsgBox("Please fill-up all fields!", MsgBoxStyle.Exclamation, "Inventory!")
Else
Using CN As New OleDb.OleDbConnection With {.ConnectionString = "CON_STR"},
Cmd1 As New OleDb.OleDbCommand(CMDText, CN)
CN.Open()
With Cmd1.Parameters
.Add("#Monitor1", OleDb.OleDbType.VarChar).Value = txtMonitor1.Text
.Add("#Monitor2", OleDb.OleDbType.VarChar).Value = txtMonitor2.Text
End With
Found = Cmd1.ExecuteScalar()
End Using
If Found > 0 Then
' User already exists
MsgBox("User Already Exist!", MsgBoxStyle.Exclamation, "Add New User!")
Else
Dim CmdText1 As String =
("INSERT INTO Asset (Monitor1,Monitor2) VALUES (#Monitor1 ,#Monitor2)")
Using Cmd As New OleDb.OleDbCommand(CmdText1, CN)
With Cmd.Parameters
.Add("#Monitor1", OleDb.OleDbType.VarChar).Value = txtMonitor1.Text
.Add("#Monitor2", OleDb.OleDbType.VarChar).Value = txtMonitor2.Text
End With
Cmd.ExecuteNonQuery()
' User does not exist, add them
MsgBox("Records Successfully Added!", MsgBoxStyle.Information, "Add New Customer!")
txtMonitor1.Text = String.Empty
txtMonitor2.Text = String.Empty
Cmd.Parameters.Clear()
End Using
End If
End If
End Sub
In my example Code : "CON_STR" = My ConnectionString that I used to test my Code, as you did not provide any.