Union fields with time attributes have different types

[Sebastián Magrí]

I'm using a query like this

WITH aggs_1m AS (
  SELECT
    `evt`,
    `startts`
    `endts`,
    SUM(`value`) AS `value`
  FROM aggregates_per_minute
), aggs_3m AS (
  SELECT
    `evt`,
    TUMBLE_START(`endts`, INTERVAL '3' MINUTE) AS `startts`,
    TUMBLE_END(`endts`, INTERVAL '3' MINUTE) AS `endts`,
    SUM(`c`) AS `value`
  FROM aggregates_per_minute
  GROUP BY t, TUMBLE(`endts`, INTERVAL '3' MINUTE)
)
SELECT `evt`, `value`, `startts`, `endts`
FROM aggs_1m
UNION
SELECT `evt`, `value`, `startts`, `endts`
FROM aggs_3m

But it's throwing this exception

org.apache.flink.table.api.ValidationException: Union fields with time
attributes have different types.

Doesn't TUMBLE_START(somets, ...) return a TIMESTAMP of the same type?

-- 
Sebastián Ramírez Magrí