ydb/yql/essentials/tests/s-expressions/suites/ImplictCasts/NarrowStruct.yqls

(
(let config (DataSource 'config))

(let res_sink (DataSink 'result))
(let data (AsList (AsStruct '('key (Just (Int64 '12))))))
(let data (Append data (AsStruct '('key (Int64 '34)) '('value (String 'foo)))))
(let world (Write! world res_sink (Key) data '('('type))))
(let world (Commit! world res_sink))
(return world)
)