ClickHouse/docs/en/sql-reference/statements/alter/ttl.md

slug	sidebar_position	sidebar_label
/en/sql-reference/statements/alter/ttl	44	TTL

Manipulations with Table TTL

MODIFY TTL

You can change table TTL with a request of the following form:

ALTER TABLE [db.]table_name [ON CLUSTER cluster] MODIFY TTL ttl_expression;

REMOVE TTL

TTL-property can be removed from table with the following query:

ALTER TABLE [db.]table_name [ON CLUSTER cluster] REMOVE TTL

Example

Consider the table with table TTL:

CREATE TABLE table_with_ttl
(
    event_time DateTime,
    UserID UInt64,
    Comment String
)
ENGINE MergeTree()
ORDER BY tuple()
TTL event_time + INTERVAL 3 MONTH
SETTINGS min_bytes_for_wide_part = 0;

INSERT INTO table_with_ttl VALUES (now(), 1, 'username1');

INSERT INTO table_with_ttl VALUES (now() - INTERVAL 4 MONTH, 2, 'username2');

Run OPTIMIZE to force TTL cleanup:

OPTIMIZE TABLE table_with_ttl FINAL;
SELECT * FROM table_with_ttl FORMAT PrettyCompact;

Second row was deleted from table.

┌─────────event_time────┬──UserID─┬─────Comment──┐
│   2020-12-11 12:44:57 │       1 │    username1 │
└───────────────────────┴─────────┴──────────────┘

Now remove table TTL with the following query:

ALTER TABLE table_with_ttl REMOVE TTL;

Re-insert the deleted row and force the TTL cleanup again with OPTIMIZE:

INSERT INTO table_with_ttl VALUES (now() - INTERVAL 4 MONTH, 2, 'username2');
OPTIMIZE TABLE table_with_ttl FINAL;
SELECT * FROM table_with_ttl FORMAT PrettyCompact;

The TTL is no longer there, so the second row is not deleted:

┌─────────event_time────┬──UserID─┬─────Comment──┐
│   2020-12-11 12:44:57 │       1 │    username1 │
│   2020-08-11 12:44:57 │       2 │    username2 │
└───────────────────────┴─────────┴──────────────┘

See Also

• More about the TTL-expression.
• Modify column with TTL.