CREATE TABLE table_204_49 (id DECIMAL, "city" TEXT, "country" TEXT, "iata" TEXT, "icao" TEXT, "airport" TEXT, "commenced" DECIMAL, "ended" TEXT)

how long did tigerair fly into chiang mai ?
SELECT "ended" - "commenced" FROM table_204_49 WHERE "city" = 'chiang mai'
SELECT "ended" - "commenced" FROM "table_204_49" WHERE "city" = 'chiang mai'