CREATE TABLE table_203_591 (id DECIMAL, "high school" TEXT, "join\ year" TEXT, "from" TEXT, "left" TEXT, "league left to" TEXT)

what was the last school to join the genesee county b league ?
SELECT "high school" FROM table_203_591 ORDER BY "join\nyear" DESC LIMIT 1
SELECT "high school" FROM "table_203_591" ORDER BY "join\nyear" DESC NULLS LAST LIMIT 1