mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-11 08:52:06 +00:00
45 lines
1.3 KiB
Markdown
45 lines
1.3 KiB
Markdown
---
|
|
toc_priority: 50
|
|
toc_title: VIEW
|
|
---
|
|
|
|
# ALTER TABLE … MODIFY QUERY 语句 {#alter-modify-query}
|
|
|
|
当使用`ALTER TABLE … MODIFY QUERY`语句创建一个[物化视图](../create/view.md#materialized)时，可以修改`SELECT`查询。当物化视图在没有 `TO [db.]name` 的情况下创建时使用它。必须启用 `allow_experimental_alter_materialized_view_structure`设置。
|
|
|
|
如果一个物化视图使用`TO [db.]name`，你必须先 [DETACH](../detach.md) 视图。用[ALTER TABLE](index.md)修改目标表，然后 [ATTACH](../attach.md)之前分离的(`DETACH`)视图。
|
|
|
|
**示例**
|
|
|
|
```sql
|
|
CREATE TABLE src_table (`a` UInt32) ENGINE = MergeTree ORDER BY a;
|
|
CREATE MATERIALIZED VIEW mv (`a` UInt32) ENGINE = MergeTree ORDER BY a AS SELECT a FROM src_table;
|
|
INSERT INTO src_table (a) VALUES (1), (2);
|
|
SELECT * FROM mv;
|
|
```
|
|
```text
|
|
┌─a─┐
|
|
│ 1 │
|
|
│ 2 │
|
|
└───┘
|
|
```
|
|
```sql
|
|
ALTER TABLE mv MODIFY QUERY SELECT a * 2 as a FROM src_table;
|
|
INSERT INTO src_table (a) VALUES (3), (4);
|
|
SELECT * FROM mv;
|
|
```
|
|
```text
|
|
┌─a─┐
|
|
│ 6 │
|
|
│ 8 │
|
|
└───┘
|
|
┌─a─┐
|
|
│ 1 │
|
|
│ 2 │
|
|
└───┘
|
|
```
|
|
|
|
## ALTER LIVE VIEW 语句 {#alter-live-view}
|
|
|
|
`ALTER LIVE VIEW ... REFRESH` 语句刷新一个 [实时视图](../create/view.md#live-view). 参见 [强制实时视图刷新](../create/view.md#live-view-alter-refresh).
|