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87 lines
2.4 KiB
Markdown
87 lines
2.4 KiB
Markdown
---
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slug: /en/sql-reference/statements/alter/ttl
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sidebar_position: 44
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sidebar_label: TTL
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---
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# Manipulations with Table TTL
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## MODIFY TTL
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You can change [table TTL](../../../engines/table-engines/mergetree-family/mergetree.md#mergetree-table-ttl) with a request of the following form:
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``` sql
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ALTER TABLE [db.]table_name [ON CLUSTER cluster] MODIFY TTL ttl_expression;
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```
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## REMOVE TTL
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TTL-property can be removed from table with the following query:
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```sql
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ALTER TABLE [db.]table_name [ON CLUSTER cluster] REMOVE TTL
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```
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**Example**
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Consider the table with table `TTL`:
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```sql
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CREATE TABLE table_with_ttl
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(
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event_time DateTime,
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UserID UInt64,
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Comment String
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)
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ENGINE MergeTree()
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ORDER BY tuple()
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TTL event_time + INTERVAL 3 MONTH
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SETTINGS min_bytes_for_wide_part = 0;
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INSERT INTO table_with_ttl VALUES (now(), 1, 'username1');
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INSERT INTO table_with_ttl VALUES (now() - INTERVAL 4 MONTH, 2, 'username2');
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```
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Run `OPTIMIZE` to force `TTL` cleanup:
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```sql
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OPTIMIZE TABLE table_with_ttl FINAL;
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SELECT * FROM table_with_ttl FORMAT PrettyCompact;
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```
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Second row was deleted from table.
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```text
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┌─────────event_time────┬──UserID─┬─────Comment──┐
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│ 2020-12-11 12:44:57 │ 1 │ username1 │
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└───────────────────────┴─────────┴──────────────┘
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```
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Now remove table `TTL` with the following query:
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```sql
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ALTER TABLE table_with_ttl REMOVE TTL;
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```
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Re-insert the deleted row and force the `TTL` cleanup again with `OPTIMIZE`:
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```sql
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INSERT INTO table_with_ttl VALUES (now() - INTERVAL 4 MONTH, 2, 'username2');
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OPTIMIZE TABLE table_with_ttl FINAL;
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SELECT * FROM table_with_ttl FORMAT PrettyCompact;
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```
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The `TTL` is no longer there, so the second row is not deleted:
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```text
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┌─────────event_time────┬──UserID─┬─────Comment──┐
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│ 2020-12-11 12:44:57 │ 1 │ username1 │
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│ 2020-08-11 12:44:57 │ 2 │ username2 │
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└───────────────────────┴─────────┴──────────────┘
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```
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**See Also**
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- More about the [TTL-expression](../../../sql-reference/statements/create/table.md#ttl-expression).
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- Modify column [with TTL](../../../sql-reference/statements/alter/column.md#alter_modify-column).
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