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docs/en/sql-reference/statements/create/view.md
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@ -85,6 +85,10 @@ Also note, that `materialized_views_ignore_errors` set to `true` by default for
If you specify `POPULATE`, the existing table data is inserted into the view when creating it, as if making a `CREATE TABLE ... AS SELECT ...` . Otherwise, the query contains only the data inserted in the table after creating the view. We **do not recommend** using `POPULATE`, since data inserted in the table during the view creation will not be inserted in it.
:::note
Given that `POPULATE` works like `CREATE TABLE ... AS SELECT ...` it is not supported in ClickHouse Cloud. Instead a separate `INSERT ... SELECT` can be used.
:::
A `SELECT` query can contain `DISTINCT`, `GROUP BY`, `ORDER BY`, `LIMIT`. Note that the corresponding conversions are performed independently on each block of inserted data. For example, if `GROUP BY` is set, data is aggregated during insertion, but only within a single packet of inserted data. The data won’t be further aggregated. The exception is when using an `ENGINE` that independently performs data aggregation, such as `SummingMergeTree`.
The execution of [ALTER](/docs/en/sql-reference/statements/alter/view.md) queries on materialized views has limitations, for example, you can not update the `SELECT` query, so this might be inconvenient. If the materialized view uses the construction `TO [db.]name`, you can `DETACH` the view, run `ALTER` for the target table, and then `ATTACH` the previously detached (`DETACH`) view.