ADODB.Recordset Invalid Column Name VB6

I'm trying to limit the recordset retuned in the sub below by a
variable called vcnumber. I'm not sure what the problem is but I keep
getting the error "Invalid Column Name" when I set sqlstring to "select
* from vc_names where vc_case_number =" & vcnumber. If I don't try to
limit the recordset returned and just set sqlstring to "select * from
vc_names", it works. If there is another\better way to do this, I am
open to suggestions. Thanks!
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Public Sub populatename()
Dim adoConnection As ADODB.Connection
Dim adoRecordset As ADODB.Recordset
Dim connectString As String
Dim sqlstring As String
Set adoConnection = CreateObject("ADODB.Connection")
Set adoRecordset = CreateObject("ADODB.Recordset")
connectString = "Provider=SQLOLEDB.1;Password=password;Persist Security
Info=True;User ID=user;Initial Catalog=db;Data Source=server"
adoConnection.Open connectString
sqlstring = "select * from vc_names where vc_case_number =" & vcnumber
adoRecordset.Open sqlstring, adoConnection, adOpenDynamic,
adLockOptimistic
Do Until adoRecordset.EOF
List2.AddItem adoRecordset!first_name & " " & adoRecordset!middle_name
& " " & adoRecordset!last_name
adoRecordset.MoveNext
Loop
adoRecordset.Close
adoConnection.Close
Set adoRecordset = Nothing
Set adoConnection = Nothing
End Sub
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========================if vs_case_number is a char field, remember to add quotes i.e.
sqlstring = "select * from vc_names where vc_case_number = '" &
vcnumber & "'"