incorrect except join query

[sundy-li]

🐳 :) create table a as select null, 3;

CREATE TABLE a
AS
    SELECT NULL, 3

1 row written in 0.100 sec. Processed 1 row, 1 B (10 rows/s, 10 B/s)

🐳 :) create table b as select null, 3;

CREATE TABLE b
AS
    SELECT NULL, 3

1 row written in 0.095 sec. Processed 1 row, 1 B (10.53 rows/s, 10 B/s)

🐳 :) select * from a except select * from b union all select * from b except select * from a;

should have empty results

@Dousir9

Originally posted by @sundy-li in #17100 (comment)