CREATE TABLE table_204_598 (id NUMBER, "name" CLOB, "state of residence" CLOB, "took office" CLOB, "left office" CLOB, "president served under" CLOB)

how many years did david plouffe serve ?
SELECT "left office" - "took office" FROM table_204_598 WHERE "name" = 'david plouffe'
SELECT "left office" - "took office" FROM "table_204_598" WHERE "name" = 'david plouffe'