NOT IN의 하위 쿼리에 NULL이 있으면 전체 SQL 결과가 항상 비어있는 이유

Schema

CREATE TABLE members (
  id INT NOT NULL PRIMARY KEY auto_increment,
  name TEXT,
  age INT,
  city TEXT,
  class_name TEXT
);

INSERT INTO members VALUES
    (1, 'brown', 22, 'tokyo', 'A'),
    (2, 'rally', 19, 'saitama', 'A'),
    (3, 'boggie', 21, 'chiba', 'A'),
    (4, 'saito', 22, 'tokyo', 'B'),
    (5, 'tashiro', NULL, 'tokyo', 'B'),
    (6, 'yamada', 18, 'tokyo', 'B'),
    (7, 'izumi', 19, 'chiba', 'B'),
    (8, 'takeda', 20, 'chiba', 'B'),    
    (9, 'ishikawa', 19, 'kanagawa', 'B');

Query

WITH
   members_A AS ( SELECT * FROM members WHERE class_name = 'A')

SELECT * FROM members_A
WHERE age NOT IN (SELECT age FROM members WHERE class_name = 'B' AND city = 'tokyo')

예상 Results

실제 Results

SELECT *
FROM members_A
WHERE age NOT IN (22,NULL,18)

SELECT *
FROM members_A
WHERE NOT age IN (22,NULL,18)

SELECT *
FROM members_A
WHERE NOT ( (age=22) OR (age=NULL) OR (age=18) )

SELECT *
FROM members_A
WHERE NOT ( (age=22) AND NOT (age=NULL) AND NOT (age=18) )

SELECT *
FROM members_A
WHERE NOT ( (age<>22) AND (age<>NULL) AND (age<>18) )

SELECT *
FROM members_A
WHERE NOT ( (age<>22) AND (unknown) AND (age<>18) )

SELECT *
FROM members_A
WHERE false または unknown

WITH
   members_A AS ( SELECT * FROM members WHERE class_name = 'A')

SELECT * FROM members_A
WHERE NOT EXISTS (
  SELECT age 
  FROM members AS members_B
  WHERE class_name = 'B' 
        AND city = 'tokyo'
        AND members_B.age = members_A.age
)

SELECT * FROM members_A
WHERE NOT EXISTS (
  SELECT age 
  FROM members AS members_B
  WHERE class_name = 'B' 
        AND city = 'tokyo'
        AND NULL = members_A.age
)

SELECT * FROM members_A
WHERE NOT EXISTS (
  SELECT age 
  FROM members AS members_B
  WHERE class_name = 'B' 
        AND city = 'tokyo'
        AND unknown
)

SELECT * FROM members_A
WHERE true

참조

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