 what's the date where visitor is phoenix suns and record is 31–30
CREATE TABLE "march" (
  "num" real,
  "date" text,
  "visitor" text,
  "score" text,
  "home" text,
  "leading_scorer" text,
  "attendance" text,
  "record" text,
  "streak" text
);
SELECT "date" FROM "march" WHERE "visitor"='Phoenix Suns' AND "record"='31–30';