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' ;
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