即时变更

SET apply_mutations_on_fly = 1;

CREATE TABLE test_on_fly_mutations (id UInt64, v String)
ENGINE = MergeTree ORDER BY id;

-- 禁用变更的后台物化，以展示
-- 未启用即时变更时的默认行为
SYSTEM STOP MERGES test_on_fly_mutations;
SET mutations_sync = 0;

-- 向新表中插入若干行
INSERT INTO test_on_fly_mutations VALUES (1, 'a'), (2, 'b'), (3, 'c');

-- 更新行的值
ALTER TABLE test_on_fly_mutations UPDATE v = 'd' WHERE id = 1;
ALTER TABLE test_on_fly_mutations DELETE WHERE v = 'd';
ALTER TABLE test_on_fly_mutations UPDATE v = 'e' WHERE id = 2;
ALTER TABLE test_on_fly_mutations DELETE WHERE v = 'e';

-- 显式禁用即时变更
SET apply_mutations_on_fly = 0;

SELECT id, v FROM test_on_fly_mutations ORDER BY id;

┌─id─┬─v─┐
│  1 │ a │
│  2 │ b │
│  3 │ c │
└────┴───┘

-- 启用即时变更
SET apply_mutations_on_fly = 1;

SELECT id, v FROM test_on_fly_mutations ORDER BY id;

┌─id─┬─v─┐
│  3 │ c │
└────┴───┘