text: DROP TABLE IF EXISTS mv_source;
  DROP TABLE IF EXISTS mv_target;
  
  CREATE TABLE mv_source (`a` UInt64) ENGINE = MergeTree ORDER BY tuple();
  CREATE TABLE mv_target (`a` UInt64) ENGINE = MergeTree ORDER BY tuple();
  
  CREATE MATERIALIZED VIEW mv TO mv_target AS SELECT * FROM mv_source;
  
  INSERT INTO mv_source VALUES (1);
  
  ALTER TABLE mv_target ADD COLUMN b UInt8;
  INSERT INTO mv_source VALUES (1),(2),(3);
  
  SELECT * FROM mv ORDER BY a;
  SELECT * FROM mv_target ORDER BY a;
  