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> Documentation for ALTER TABLE ... DELETE Statement

# ALTER TABLE ... DELETE Statement

```sql theme={null}
ALTER TABLE [db.]table [ON CLUSTER cluster] DELETE WHERE filter_expr
```

Deletes data matching the specified filtering expression. Implemented as a [mutation](/reference/statements/alter#mutations).

<Note>
  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](/reference/statements/delete), which performs a lightweight delete and can be considerably faster.
</Note>

The `filter_expr` must be of type `UInt8`. The query deletes rows in the table for which this expression takes a non-zero value.

One query can contain several commands separated by commas.

The synchronicity of the query processing is defined by the [mutations\_sync](/reference/settings/session-settings#mutations_sync) setting. By default, it is asynchronous.

**See also**

* [Mutations](/reference/statements/alter#mutations)
* [Synchronicity of ALTER Queries](/reference/statements/alter#synchronicity-of-alter-queries)
* [mutations\_sync](/reference/settings/session-settings#mutations_sync) setting

<h2 id="related-content">
  Related content
</h2>

* Blog: [Handling Updates and Deletes in ClickHouse](https://clickhouse.com/blog/handling-updates-and-deletes-in-clickhouse)