What kind of IHSAA Class has a School of decatur central?
CREATE TABLE "membership" (
  "school" text,
  "location" text,
  "mascot" text,
  "enrollment" real,
  "ihsaa_class" text,
  "county" text,
  "year_joined" real,
  "previous_conference" text
);
SELECT "ihsaa_class" FROM "membership" WHERE "school"='decatur central';