lead

lead

정렬된 프레임 안에서 현재 행보다 오프셋(row)만큼 뒤의 행에서 평가된 값을 반환하는 윈도우 함수예요. 이 함수는 leadInFrame와 비슷하지만, 항상 ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING 프레임을 사용합니다.

출처: 문서

본문

구문(Syntax)

lead(x[, offset[, default]])
  OVER ([[PARTITION BY grouping_column] [ORDER BY sorting_column]] | [window_name])
FROM table_name
WINDOW window_name as ([[PARTITION BY grouping_column] [ORDER BY sorting_column])

윈도우 함수 구문에 대한 자세한 내용은 윈도우 함수 - 구문을 참고하세요.

인자(Parameters)

• x — 컬럼 이름.
• offset — 적용할 오프셋. (U)Int*. (선택, 기본값 1).
• default — 계산된 행이 윈도우 프레임 경계를 벗어날 때 반환할 값. (선택, 생략하면 컬럼 타입의 기본값).

반환 값(Returned value)

• 정렬된 프레임 안에서 현재 행보다 오프셋(row)만큼 뒤의 행에서 평가된 값.

예시(Example)

이 예시는 노벨상 수상자들의 역사 데이터를 보면서 lead 함수로 물리학 분야의 연이은 수상자 목록을 반환해요.

쿼리(Query)

CREATE OR REPLACE VIEW nobel_prize_laureates
AS SELECT *
FROM file('nobel_laureates_data.csv');

쿼리(Query)

SELECT
    fullName,
    lead(year, 1, year) OVER (PARTITION BY category ORDER BY year ASC
      ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
    ) AS year,
    category,
    motivation
FROM nobel_prize_laureates
WHERE category = 'physics'
ORDER BY year DESC
LIMIT 9

쿼리(Query)

   ┌─fullName─────────┬─year─┬─category─┬─motivation─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
1. │ Anne L Huillier  │ 2023 │ physics  │ for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter                     │
2. │ Pierre Agostini  │ 2023 │ physics  │ for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter                     │
3. │ Ferenc Krausz    │ 2023 │ physics  │ for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter                     │
4. │ Alain Aspect     │ 2022 │ physics  │ for experiments with entangled photons establishing the violation of Bell inequalities and  pioneering quantum information science │
5. │ Anton Zeilinger  │ 2022 │ physics  │ for experiments with entangled photons establishing the violation of Bell inequalities and  pioneering quantum information science │
6. │ John Clauser     │ 2022 │ physics  │ for experiments with entangled photons establishing the violation of Bell inequalities and  pioneering quantum information science │
7. │ Giorgio Parisi   │ 2021 │ physics  │ for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales                │
8. │ Klaus Hasselmann │ 2021 │ physics  │ for the physical modelling of Earths climate quantifying variability and reliably predicting global warming                        │
9. │ Syukuro Manabe   │ 2021 │ physics  │ for the physical modelling of Earths climate quantifying variability and reliably predicting global warming                        │
   └──────────────────┴──────┴──────────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

더 알아보기 (Learn more)

• leadInFrame
• lag
• 윈도우 함수 - 구문 (Window Functions - Syntax)