CREATE TABLE table_204_542 (id DECIMAL, "season" TEXT, "competition" TEXT, "round" TEXT, "club" TEXT, "home" TEXT, "away" TEXT, "aggregate" TEXT)

what is the number of countries that played during the 2011-12 uefa europa league ?
SELECT COUNT("club") FROM table_204_542 WHERE "season" = '2011-12'
SELECT COUNT("club") FROM "table_204_542" WHERE "season" = '2011-12'