CREATE TABLE table_201_21 (id DECIMAL, "year" DECIMAL, "title" TEXT, "role" TEXT, "notes" TEXT)

which role is the most common from all the titles ?
SELECT "role" FROM table_201_21 GROUP BY "role" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "role" FROM "table_201_21" GROUP BY "role" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1