CREATE TABLE table_204_501 (id DECIMAL, "institution" TEXT, "location" TEXT, "nickname" TEXT, "founded" DECIMAL, "type" TEXT, "enrollment" DECIMAL, "joined" DECIMAL)

which school has the least number of students attending it ?
SELECT "institution" FROM table_204_501 ORDER BY "enrollment" LIMIT 1
SELECT "institution" FROM "table_204_501" ORDER BY "enrollment" NULLS FIRST LIMIT 1