TTL GROUP BY Examples

Example with MergeTree table

CREATE TABLE test_ttl_group_by
(
    `key` UInt32,
    `ts` DateTime,
    `value` UInt32,
    `min_value` UInt32 DEFAULT value,
    `max_value` UInt32 DEFAULT value
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(ts)
ORDER BY (key, toStartOfDay(ts))
TTL ts + interval 30 day 
    GROUP BY key, toStartOfDay(ts) 
    SET value = sum(value), 
    min_value = min(min_value), 
    max_value = max(max_value), 
    ts = min(toStartOfDay(ts));

During TTL merges Clickhouse re-calculates values of columns in the SET section.

GROUP BY section should be a prefix of a table’s ORDER BY.

-- stop merges to demonstrate data before / after 
-- a rolling up
SYSTEM STOP TTL MERGES test_ttl_group_by;
SYSTEM STOP MERGES test_ttl_group_by;

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() + number,
    1
FROM numbers(100);

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() - interval 60 day + number,
    2
FROM numbers(100);

SELECT
    toYYYYMM(ts) AS m,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY m;
┌──────m─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 202102      100         200               2               2 
 202104      100         100               1               1 
└────────┴─────────┴────────────┴────────────────┴────────────────┘

SYSTEM START TTL MERGES test_ttl_group_by;
SYSTEM START MERGES test_ttl_group_by;
OPTIMIZE TABLE test_ttl_group_by FINAL;

SELECT
    toYYYYMM(ts) AS m,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY m;
┌──────m─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 202102        5         200               2               2 
 202104      100         100               1               1 
└────────┴─────────┴────────────┴────────────────┴────────────────┘

As you can see 100 rows were rolled up into 5 rows (key has 5 values) for rows older than 30 days.

Example with SummingMergeTree table

CREATE TABLE test_ttl_group_by
(
    `key1` UInt32,
    `key2` UInt32,
    `ts` DateTime,
    `value` UInt32,
    `min_value` SimpleAggregateFunction(min, UInt32) 
                                       DEFAULT value,
    `max_value` SimpleAggregateFunction(max, UInt32) 
                                       DEFAULT value
)
ENGINE = SummingMergeTree
PARTITION BY toYYYYMM(ts)
PRIMARY KEY (key1, key2, toStartOfDay(ts))
ORDER BY (key1, key2, toStartOfDay(ts), ts)
TTL ts + interval 30 day 
    GROUP BY key1, key2, toStartOfDay(ts) 
    SET value = sum(value), 
    min_value = min(min_value), 
    max_value = max(max_value), 
    ts = min(toStartOfDay(ts));

-- stop merges to demonstrate data before / after 
-- a rolling up
SYSTEM STOP TTL MERGES test_ttl_group_by;
SYSTEM STOP MERGES test_ttl_group_by;

INSERT INTO test_ttl_group_by (key1, key2, ts, value)
SELECT
    1,
    1,
    toStartOfMinute(now() + number*60),
    1
FROM numbers(100);

INSERT INTO test_ttl_group_by (key1, key2, ts, value)
SELECT
    1,
    1,
    toStartOfMinute(now() + number*60),
    1
FROM numbers(100);

INSERT INTO test_ttl_group_by (key1, key2, ts, value)
SELECT
    1,
    1,
    toStartOfMinute(now() + number*60 - toIntervalDay(60)),
    2
FROM numbers(100);

INSERT INTO test_ttl_group_by (key1, key2, ts, value)
SELECT
    1,
    1,
    toStartOfMinute(now() + number*60 - toIntervalDay(60)),
    2
FROM numbers(100);

SELECT
    toYYYYMM(ts) AS m,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY m;

┌──────m─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 202102      200         400               2               2 
 202104      200         200               1               1 
└────────┴─────────┴────────────┴────────────────┴────────────────┘

SYSTEM START TTL MERGES test_ttl_group_by;
SYSTEM START MERGES test_ttl_group_by;
OPTIMIZE TABLE test_ttl_group_by FINAL;

SELECT
    toYYYYMM(ts) AS m,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY m;

┌──────m─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 202102        1         400               2               2 
 202104      100         200               1               1 
└────────┴─────────┴────────────┴────────────────┴────────────────┘

During merges Clickhouse re-calculates ts columns as min(toStartOfDay(ts)). It’s possible only for the last column of SummingMergeTree ORDER BY section ORDER BY (key1, key2, toStartOfDay(ts), ts) otherwise it will break the order of rows in the table.

Multilevel TTL Group by

CREATE TABLE test_ttl_group_by
(
    `key` UInt32,
    `ts` DateTime,
    `value` UInt32,
    `min_value` UInt32 DEFAULT value,
    `max_value` UInt32 DEFAULT value
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(ts)
ORDER BY (key, toStartOfWeek(ts), toStartOfDay(ts), toStartOfHour(ts))
TTL 
ts + interval 1 hour 
GROUP BY key, toStartOfWeek(ts), toStartOfDay(ts), toStartOfHour(ts) 
    SET value = sum(value), 
    min_value = min(min_value), 
    max_value = max(max_value), 
    ts = min(toStartOfHour(ts)),
ts + interval 1 day 
GROUP BY key, toStartOfWeek(ts), toStartOfDay(ts) 
    SET value = sum(value), 
    min_value = min(min_value), 
    max_value = max(max_value), 
    ts = min(toStartOfDay(ts)),
ts + interval 30 day 
GROUP BY key, toStartOfWeek(ts) 
    SET value = sum(value), 
    min_value = min(min_value), 
    max_value = max(max_value), 
    ts = min(toStartOfWeek(ts));
    
SYSTEM STOP TTL MERGES test_ttl_group_by;
SYSTEM STOP MERGES test_ttl_group_by;

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() + number,
    1
FROM numbers(100);

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() - interval 2 hour + number,
    2
FROM numbers(100);    

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() - interval 2 day + number,
    3
FROM numbers(100);    

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() - interval 2 month + number,
    4
FROM numbers(100); 

SELECT
    toYYYYMMDD(ts) AS d,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY d
ORDER BY d;

┌────────d─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 20210616      100         400               4               4 
 20210814      100         300               3               3 
 20210816      200         300               1               2 
└──────────┴─────────┴────────────┴────────────────┴────────────────┘

SYSTEM START TTL MERGES test_ttl_group_by;
SYSTEM START MERGES test_ttl_group_by;
OPTIMIZE TABLE test_ttl_group_by FINAL;

SELECT
    toYYYYMMDD(ts) AS d,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY d
ORDER BY d;

┌────────d─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 20210613        5         400               4               4 
 20210814        5         300               3               3 
 20210816      105         300               1               2 
└──────────┴─────────┴────────────┴────────────────┴────────────────┘

TTL GROUP BY + DELETE

CREATE TABLE test_ttl_group_by
(
    `key` UInt32,
    `ts` DateTime,
    `value` UInt32,
    `min_value` UInt32 DEFAULT value,
    `max_value` UInt32 DEFAULT value
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(ts)
ORDER BY (key, toStartOfDay(ts))
TTL 
ts + interval 180 day,
ts + interval 30 day 
    GROUP BY key, toStartOfDay(ts) 
    SET value = sum(value), 
    min_value = min(min_value), 
    max_value = max(max_value), 
    ts = min(toStartOfDay(ts));

-- stop merges to demonstrate data before / after 
-- a rolling up
SYSTEM STOP TTL MERGES test_ttl_group_by;
SYSTEM STOP MERGES test_ttl_group_by;

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() + number,
    1
FROM numbers(100);

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() - interval 60 day + number,
    2
FROM numbers(100);    

INSERT INTO test_ttl_group_by (key, ts, value)
SELECT
    number % 5,
    now() - interval 200 day + number,
    3
FROM numbers(100);  

SELECT
    toYYYYMM(ts) AS m,
    count(),
    sum(value),
    min(min_value),
    max(max_value)
FROM test_ttl_group_by
GROUP BY m;

┌──────m─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 202101      100         300               3               3 
 202106      100         200               2               2 
 202108      100         100               1               1 
└────────┴─────────┴────────────┴────────────────┴────────────────┘

SYSTEM START TTL MERGES test_ttl_group_by;
SYSTEM START MERGES test_ttl_group_by;
OPTIMIZE TABLE test_ttl_group_by FINAL;

┌──────m─┬─count()─┬─sum(value)─┬─min(min_value)─┬─max(max_value)─┐
 202106        5         200               2               2 
 202108      100         100               1               1 
└────────┴─────────┴────────────┴────────────────┴────────────────┘

Last modified 2021.08.24 : Adjusted code. (a6f74294)