CREATE TABLE table_204_975 (id DECIMAL, "year" DECIMAL, "competition" TEXT, "location" TEXT, "event" TEXT, "final-rank" TEXT, "final-score" DECIMAL, "qualifying rank" DECIMAL, "qualifying score" DECIMAL)

which competition took place in 2008 but had only one event ?
SELECT "competition" FROM table_204_975 GROUP BY "competition" HAVING COUNT("event") = 1
SELECT "competition" FROM "table_204_975" GROUP BY "competition" HAVING COUNT("event") = 1