ydb/yql/essentials/tests/s-expressions/suites/Aggregation/EmptyOptional.yql

(
(let world (block '(
  (let x (Read! world (DataSource '"yt" '"plato") (Key '('table (String '"Input"))) '('"key" '"subkey" '"value") '()))
  (let world (Left! x))
  (let table0 (Right! x))
  (let output (block '(
    (let select (block '(
      (let core (block '(
        (let select (block '(
          (let core table0)
          (let core (FlatMap core (lambda '(row) (block '(
            (let res (Struct))
            (let res (AddMember res '"key" (Member row '"key")))
            (let res (AddMember res '"subkey" (Member row '"subkey")))
            (let res (AddMember res '"value" (Cast (Member row '"value") 'Double)))
            (let res (AsList res))
            (return res)
          )))))
          (return core)
        )))
        (return select)
      )))
      (let core (block '(
        (let Sum1_create (lambda '(row) (Member row '"value")))
        (let Sum1_update (lambda '(row state) (OptionalReduce state (Member row '"value") (lambda '(a b) (+ a b)))))
        (let Sum1_save (lambda '(state) state))
        (let Sum1_load (lambda '(item) item))
        (let Sum1_merge (lambda '(a b) (OptionalReduce a b (lambda '(a b) (+ a b)))))
        (let Sum1_finish (lambda '(state) state))
        (return (Aggregate core '('"key") '('('Sum1 (AggregationTraits (ListItemType (TypeOf core)) Sum1_create Sum1_update Sum1_save Sum1_load Sum1_merge Sum1_finish (Null))))))
      )))
      (let core (FlatMap core (lambda '(row) (block '(
        (let res (Struct))
        (let res (AddMember res '"key" (Member row '"key")))
        (let res (AddMember res '"subkey" (String '"")))
        (let res (AddMember res '"value" (Member row 'Sum1)))
        (let res (AsList res))
        (return res)
      )))))
      (return core)
    )))
    (let select (Sort select (Bool 'true) (lambda '(row) (Member row '"key"))))
    (return select)
  )))
  (let world (block '(
    (let result_sink (DataSink 'result))
    (let world (Write! world result_sink (Key) output '('('type) '('autoref) '('columns '('"key" '"subkey" '"value")))))
    (return (Commit! world result_sink))
  )))
  (return world)
)))
(let world (block '(
  (let plato_sink (DataSink '"yt" '"plato"))
  (let world (Commit! world plato_sink))
  (return world)
)))
(return world)
)