If you are wanting ID's to be unique, you might want to think about making it a primary key. Thus making it not possible to have multiples. Then you can wrap your insert in a try catch, the client will handle the "No duplicate keys" message.
'sqls is a string
'cmd is a command builder
sqls = "SELECT * FROM employees WHERE id = '" & textbox1.text & "'"
cmd = New CommandBuilder(sqls,connection)
If cmd.ExecuteNonQuery = False Then
MsgBox("ID not found")