Predictive Text - How To Display Records From Database Into DropdownList

How to query a record in vb.net using combo or textbox via linq to sql like the search engine? Just like when you search in google or youtube, once you typed in the initial string on the textbox or combo box it will show a drop-down list. I tried to use it in my application using linq method but the problem is it would duplicate on the first string that you entered on the dropdownlist if that record exist on your database after you press the space key. I used the code below which duplicates the records on the drop-down list when you type in your string after the space key.

I just want it to be like in any search engine that when you type in the string or your initial string, it will display on the drop-down list all the records from the database that contains the string you entered without duplication. In my case, I'm trying to query a name from my database. This is how it should work, For example, if you type an initial string in the textbox or combo box a named 'Mark', it should display all the names from the database containing 'Mark' into the drop-down list before it changes into its final string that you entered.

Here is the codes I used:
Private Sub ComboBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles
ComboBox1.TextChanged
Dim db As New MultipleDatabaseOperationDataContext
Dim search As String
search = ComboBox1.Text
[Code] .....