--- sidebar_position: 50 sidebar_label: 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).