CREATE TABLE entity_events
(
    `datetime` DateTime,
    `event` UInt8,
    `entity1` String,
    `entity2` String,
    `entity3` String
)
ENGINE = MergeTree()
ORDER BY datetime;

CREATE MATERIALIZED VIEW user_trace_pool
ENGINE = AggregatingMergeTree
PARTITION BY tuple()
ORDER BY id POPULATE AS
SELECT
    cityHash64(entity1, entity2, entity3) AS id,
    groupArrayState((event, datetime)) AS events
FROM
(
    SELECT
        any(datetime) AS datetime,
        event,
        entity1,
        entity2,
        entity3
    FROM entity_events
    GROUP BY (event, entity1, entity2, entity3)
)
GROUP BY id;


insert into entity_events values ('2020-09-20 00:00:00', 1, 'a', 'a', 'a');
insert into entity_events values ('2020-09-20 00:00:01', 1, 'a', 'a', 'a');

SELECT
    id,
    groupArrayMerge(events) AS e
FROM user_trace_pool
GROUP BY id;

┌───────────────────id─┬─e─────────────────────────────────────────────────────┐
│ 11022927171530759889 │ [(1,'2020-09-20 00:00:01'),(1,'2020-09-20 00:00:00')] │
└──────────────────────┴───────────────────────────────────────────────────────┘