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35 lines
1.7 KiB
Markdown
35 lines
1.7 KiB
Markdown
---
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slug: /en/sql-reference/statements/alter/delete
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sidebar_position: 39
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sidebar_label: DELETE
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---
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# ALTER TABLE … DELETE Statement
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``` sql
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ALTER TABLE [db.]table [ON CLUSTER cluster] DELETE WHERE filter_expr
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```
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Deletes data matching the specified filtering expression. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md#mutations).
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:::note
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The `ALTER TABLE` prefix makes this syntax different from most other systems supporting SQL. It is intended to signify that unlike similar queries in OLTP databases this is a heavy operation not designed for frequent use. `ALTER TABLE` is considered a heavyweight operation that requires the underlying data to be merged before it is deleted. For MergeTree tables, consider using the [`DELETE FROM` query](/docs/en/sql-reference/statements/delete.md), which performs a lightweight delete and can be considerably faster.
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:::
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The `filter_expr` must be of type `UInt8`. The query deletes rows in the table for which this expression takes a non-zero value.
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One query can contain several commands separated by commas.
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The synchronicity of the query processing is defined by the [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting. By default, it is asynchronous.
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**See also**
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- [Mutations](/docs/en/sql-reference/statements/alter/index.md#mutations)
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- [Synchronicity of ALTER Queries](/docs/en/sql-reference/statements/alter/index.md#synchronicity-of-alter-queries)
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- [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting
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## Related content
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- Blog: [Handling Updates and Deletes in ClickHouse](https://clickhouse.com/blog/handling-updates-and-deletes-in-clickhouse)
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