UNION, UNION ALL, 교집합 , 차집합

UNION =중복 제거
UNION ALL = 중복 포함

SELECT절에서 가져오는 컬럼의 수가 같아야 함
ORDER BY는 쿼리 가장 마지막에 작성가능\

 

SELECT
FROM
UNION
SELECT
FROM

UNION ALL : 중복된 값도 같이 붙임

SELECT
FROM
UNION ALL
SELECT
FROM

교집합

교집합 INTERSECT
INNER JOIN

차집합

SELECT
FROM
LEFT JOIN
ON t1.z
WHERE t2.컬럼 IS NULL;

 

 

mission 1)
SELECT DISTINCT type
FROM mypokemon
UNION
SELECT DISTINCT type
FROM friendpokemon;

 

mission 2)
SELECT number, name, 'my' AS whose
FROM mypokemon
WHERE type='grass'
UNION ALL
SELECT number, name, "friend's" AS whose
FROM friendpokemon
WHERE type='grass' ;