August 2022
Beginner to intermediate
436 pages
9h 43m
Korean
Content preview from SQL로 시작하는 데이터 분석
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315
6
장
이상 탐지
실무에서 이렇게 아주 작은 차이는 그리 중요하지 않은 경우가 대부분이므로 어떤 표준편차 함
수를 사용하든 상관없습니다.
이제 이 함수들을 사용해 데이터셋의 각 값과 평균 간의 차이를 표준편차 단위로 표현해봅시
다. 이 값은
z
-점수
z
-
score
라고 부르며 데이터를 표준화하는 데 사용합니다. 평균보다 높은 값은
z
-점수가 양수이고 평균보다 낮은 값은
z
-점수가 음수입니다. [그림
6
-
2
]는 정규 분포에서
z
-점수와 표준편차의 관계를 나타냅니다.
평균
표준편차
z
-점수
그림
6-2
정규 분포에서의 표준편차와
z
-점수
지진 규모에 대한
z
-점수를 알아보기 위해 먼저 서브쿼리에서 전체 데이터셋의 평균과 표준편
차를 계산합니다. 그리고 이 서브쿼리의 결과를 활용해
z
-점수를 구한 후, 다시 전체 데이터셋
과 카티션
JOIN
을 수행하면
earthquakes
테이블의 각 행마다 지진 규모 값의
z
-점수뿐 아니
라 전체 데이터셋의 평균, 전체 표준편차까지 한 번에 출력됩니다. 대부분의 데이터베이스에서
는 카티션
JOIN
에서도
JOIN
조건을 반드시 명시해야 하므로
1
=
1
을 조건으로 사용합니다.
외부쿼리에서는 각 행의 규모 값에서 평균을 뺀 뒤 표준편차로 나눠
z
-점수를 계산합니다.
316
SQL로 시작하는 데이터 분석
SELECT
a.place, a.mag
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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.