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45 lines
1.4 KiB
Markdown
45 lines
1.4 KiB
Markdown
---
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sidebar_position: 50
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sidebar_label: VIEW
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---
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# ALTER TABLE … MODIFY QUERY Statement {#alter-modify-query}
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You can modify `SELECT` query that was specified when a [materialized view](../create/view.md#materialized) was created with the `ALTER TABLE … MODIFY QUERY` statement. Use it when the materialized view was created without the `TO [db.]name` clause. The `allow_experimental_alter_materialized_view_structure` setting must be enabled.
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If a materialized view uses the `TO [db.]name` construction, you must [DETACH](../detach.md) the view, run [ALTER TABLE](index.md) query for the target table, and then [ATTACH](../attach.md) the previously detached (`DETACH`) view.
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**Example**
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```sql
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CREATE TABLE src_table (`a` UInt32) ENGINE = MergeTree ORDER BY a;
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CREATE MATERIALIZED VIEW mv (`a` UInt32) ENGINE = MergeTree ORDER BY a AS SELECT a FROM src_table;
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INSERT INTO src_table (a) VALUES (1), (2);
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SELECT * FROM mv;
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```
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```text
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┌─a─┐
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│ 1 │
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│ 2 │
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└───┘
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```
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```sql
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ALTER TABLE mv MODIFY QUERY SELECT a * 2 as a FROM src_table;
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INSERT INTO src_table (a) VALUES (3), (4);
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SELECT * FROM mv;
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```
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```text
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┌─a─┐
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│ 6 │
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│ 8 │
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└───┘
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┌─a─┐
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│ 1 │
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│ 2 │
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└───┘
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```
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## ALTER LIVE VIEW Statement {#alter-live-view}
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`ALTER LIVE VIEW ... REFRESH` statement refreshes a [Live view](../create/view.md#live-view). See [Force Live View Refresh](../create/view.md#live-view-alter-refresh).
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