CREATE TABLE table_203_501 (id DECIMAL, "title" TEXT, "genre" TEXT, "sub\\u00addivisions" TEXT, "libretto" TEXT, "premiere date" TEXT, "place ,  theatre" TEXT)

in which city did the most operettas premiere ?
SELECT "place, theatre" FROM table_203_501 GROUP BY "place, theatre" ORDER BY COUNT("title") DESC LIMIT 1
SELECT "place, theatre" FROM "table_203_501" GROUP BY "place, theatre" ORDER BY COUNT("title") DESC NULLS LAST LIMIT 1