CREATE TABLE table_31803 ("Year" FLOAT, "Date" TEXT, "Event" TEXT, "Days" TEXT, "Stages" TEXT, "Acts" TEXT)

When is the Monsters of Rock show with 12 bands?
SELECT "Date" FROM table_31803 WHERE "Event" = 'monsters of rock' AND "Acts" = '12 bands'
SELECT "Date" FROM "table_31803" WHERE "Acts" = '12 bands' AND "Event" = 'monsters of rock'