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28 lines
1.2 KiB
Markdown
28 lines
1.2 KiB
Markdown
---
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toc_priority: 39
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toc_title: DELETE
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---
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# ALTER TABLE … DELETE Statement {#alter-mutations}
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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](../../../sql-reference/statements/alter/index.md#mutations).
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!!! note "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.
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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](../../../operations/settings/settings.md#mutations_sync) setting. By default, it is asynchronous.
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**See also**
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- [Mutations](../../../sql-reference/statements/alter/index.md#mutations)
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- [Synchronicity of ALTER Queries](../../../sql-reference/statements/alter/index.md#synchronicity-of-alter-queries)
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- [mutations_sync](../../../operations/settings/settings.md#mutations_sync) setting
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