When did Peter Butler leave his team?
CREATE TABLE "managerial_changes" (
  "team" text,
  "outgoing_manager" text,
  "date_outgoing" text,
  "reason_of_departure" text,
  "replaced_by" text,
  "date_of_replacement" text
);
SELECT "date_outgoing" FROM "managerial_changes" WHERE "outgoing_manager"='peter butler';