CREATE TABLE table_1817 ("Club" TEXT, "First season in top division" TEXT, "Number of seasons in top division" FLOAT, "First season of current spell in top division" TEXT, "Number of seasons in Liga MX" FLOAT, "Top division titles" FLOAT)

When did the club UNAM played the first season in top division?
SELECT "First season in top division" FROM table_1817 WHERE "Club" = 'UNAM'
SELECT "First season in top division" FROM "table_1817" WHERE "Club" = 'UNAM'