Name Type Location Description
views_handler::use_group_by function core/modules/views/includes/handlers.inc Provides the handler some groupby.
views_handler_area::use_group_by function core/modules/views/handlers/views_handler_area.inc Area handlers shouldn't have groupby.
views_plugin_display::use_group_by function core/modules/views/plugins/views_plugin_display.inc Does the display have groupby enabled?
views_handler_relationship::use_group_by function core/modules/views/handlers/views_handler_relationship.inc You can't groupby a relationship.