ClickHouse/docs/en/sql-reference/statements/alter/view.md

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50	VIEW

ALTER TABLE … MODIFY QUERY Statement

You can modify SELECT query that was specified when a materialized view 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.

If a materialized view uses the TO [db.]name construction, you must DETACH the view, run ALTER TABLE query for the target table, and then ATTACH the previously detached (DETACH) view.

Example

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;

┌─a─┐
│ 1 │
│ 2 │
└───┘

ALTER TABLE mv MODIFY QUERY SELECT a * 2 as a FROM src_table;
INSERT INTO src_table (a) VALUES (3), (4);
SELECT * FROM mv;

┌─a─┐
│ 6 │
│ 8 │
└───┘
┌─a─┐
│ 1 │
│ 2 │
└───┘

ALTER LIVE VIEW Statement

ALTER LIVE VIEW ... REFRESH statement refreshes a Live view. See Force Live View Refresh.