CREATE TABLE table_203_28 (id NUMBER, "year" NUMBER, "competition" CLOB, "venue" CLOB, "position" CLOB, "event" CLOB, "notes" CLOB)

what was the only year that a 5 km event took place ?
SELECT "year" FROM table_203_28 WHERE "event" = '5 km'
SELECT "year" FROM "table_203_28" WHERE "event" = '5 km'