August 2022
Beginner to intermediate
436 pages
9h 43m
Korean
Content preview from SQL로 시작하는 데이터 분석
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51
2
장
데이터 준비
SQL
서버는
LIMIT
절을 지원하지 않으므로 비슷한 기능을 하는
top
을 사용해야 합니다.
SELECT top 1000
column_a, column_b
FROM table
;
샘플링을 하려면 랜덤 분포를 이루는
ID
필드에 특정 함수를 사용합니다. 예를 들어,
mod
함수
는 정수의 나눗셈 결과에서 몫이 아닌 나머지 값을 반환합니다.
ID
필드가 정수라면
mod
함수를
사용해 마지막 한 자리, 두 자리 또는 세 자리 이상의 숫자로 결과를 필터링할 수 있습니다.
WHERE mod(integer_order_id,100) = 6
위 코드는
mod
함수를 사용해
integer
_
order
_
id
필드의 값을
100
으로 나눈 나머지가
6
인 결
과를 모두 반환합니다. 이 방법은 전체 데이터의
1
%만 샘플링합니다. 필드에 저장된 값이 숫자
뿐 아니라 알파벳일 수도 있다면
right
함수를 사용해서
integer
_
order
_
id
필드에서 주어진
숫자만큼의 마지막 글자(오른쪽 글자)를 반환받아 필터링할 수 있습니다.
WHERE right(alphanum_order_id,1) = 'B'
위 코드는
integer
_
order
_
id
필드의 마지막 한 글자가
B
인 결과를 모두 반환합니다. 해당 필
드에서 모든 알파벳과 숫자가 비슷한 빈도로 사용됐다는 전제하에 ...
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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.