CREATE TABLE table_204_295 (id DECIMAL, "model" TEXT, "origin" TEXT, "type" TEXT, "version" TEXT, "in service" DECIMAL, "notes" TEXT)

what model was in service the least ?
SELECT "model" FROM table_204_295 ORDER BY "in service" LIMIT 1
SELECT "model" FROM "table_204_295" ORDER BY "in service" NULLS FIRST LIMIT 1