August 2022
Beginner to intermediate
436 pages
9h 43m
Korean
Content preview from SQL로 시작하는 데이터 분석
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397
8
장
복잡한 데이터셋 생성
0 12518
1 3600
2 3619
... ...
CTE
를 활용한 쿼리 결과는
4
장에서 서브쿼리를 활용한 쿼리 결과와 정확히 일치합니다. 한 쿼
리에서 여러 개의
CTE
를 사용하고 싶다면 다음 코드와 같이 콤마 (
,
)를 사용해 다수의
CTE
를
생성합니다.
WITH first_cte as
(
SELECT...
),
second_cte
as
(
SELECT...
)
SELECT...
;
CTE
는 쿼리의 실행 순서를 조정해 성능이 더 나은 코드를 구성하는 데 유용합니다. 처음에는
어렵더라도 문법에 익숙해지면 쉽게 사용할 수 있으며, 대부분의 데이터베이스에서
CTE
를 지
원하므로 활용도가 높습니다. 당장 필요하지 않더라도 평소에 사용법을 잘 익혀놓으면 분석 수
행 시 상황에 맞는 쿼리를 작성하는 데 큰 도움이 됩니다.
8.3.5
그룹 함수
이 절에서 다루는 쿼리 실행 순서와 관련된 주제는 아니지만,
UNION
을 사용하지 않고도 쿼리
하나로 비슷한 처리를 하는 간단한 방법을 알아봅니다. 대부분의 데이터베이스에서 지원하는
GROUP
BY
절의 특수한 문법으로
grouping
sets
,
cube
,
rollup
이 있습니다 (단, 레드시프트
는 지원하지 않으며,
MySQL
은
rollup
만 지원합니다 ). 이 문법들은 다양한 속성을 조합해
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.