CREATE TABLE table_204_678 (id NUMBER, "record" CLOB, "athlete" CLOB, "nation" CLOB, "venue" CLOB, "date" CLOB, "#" NUMBER)

which country is the only one to have only one record holder for pole vaulting ?
SELECT "nation" FROM table_204_678 GROUP BY "nation" HAVING COUNT(*) = 1
SELECT "nation" FROM "table_204_678" GROUP BY "nation" HAVING COUNT(*) = 1