Define a constant that contains the columns you want to return from your query. Each item in the ListView displays the contact's display name, which contains the main form of the contact's name. In Android 3.0 (API version 11) and later, the name of this column is Contacts.DISPLAY_NAME_PRIMARY; in versions previous to that, its name is Contacts.DISPLAY_NAME.
The column Contacts._ID is used by the SimpleCursorAdapter binding process. Contacts._ID and LOOKUP_KEY are used together to construct a content URI for the contact the user selects.