Подсчитывать различные значения с помощью OVER (PARTITION BY id)

Question

Можно ли подсчитать различные значения в сочетании с функциями окна, такими как OVER(PARTITION BY id)? В настоящее время мой запрос следующим образом:

SELECT congestion.date, congestion.week_nb, congestion.id_congestion, 
    congestion.id_element, 
ROW_NUMBER() OVER(
    PARTITION BY congestion.id_element 
    ORDER BY congestion.date), 
COUNT(DISTINCT congestion.week_nb) OVER(
    PARTITION BY congestion.id_element 
) AS week_count 
FROM congestion 
WHERE congestion.date >= '2014.01.01' 
AND congestion.date <= '2014.12.31' 
ORDER BY id_element, date 

Однако, когда я пытаюсь выполнить запрос, я получаю следующее сообщение об ошибке:

"COUNT(DISTINCT": "DISTINCT is not implemented for window functions" 

Answer 1

Нет, как сказано в сообщении об ошибке, DISTINCT не реализован с окнами функции. Информацию от применяют указанные this link в вашем случае вы могли бы использовать что-то вроде:

WITH uniques AS (
SELECT congestion.id_element, COUNT(DISTINCT congestion.week_nb) AS unique_references 
FROM congestion 
WHERE congestion.date >= '2014.01.01' 
AND congestion.date <= '2014.12.31' 
GROUP BY congestion.id_element 
) 

SELECT congestion.date, congestion.week_nb, congestion.id_congestion, 
    congestion.id_element, 
ROW_NUMBER() OVER(
    PARTITION BY congestion.id_element 
    ORDER BY congestion.date), 
uniques.unique_references AS week_count 
FROM congestion 
JOIN uniques USING (id_element) 
WHERE congestion.date >= '2014.01.01' 
AND congestion.date <= '2014.12.31' 
ORDER BY id_element, date 

В зависимости от ситуации, вы можете также поместить подзапрос прямо в SELECT -list:

SELECT congestion.date, congestion.week_nb, congestion.id_congestion, 
    congestion.id_element, 
ROW_NUMBER() OVER(
    PARTITION BY congestion.id_element 
    ORDER BY congestion.date), 
(SELECT COUNT(DISTINCT dist_con.week_nb) 
    FROM congestion AS dist_con 
    WHERE dist_con.date >= '2014.01.01' 
    AND dist_con.date <= '2014.12.31' 
    AND dist_con.id_element = congestion.id_element) AS week_count 
FROM congestion 
WHERE congestion.date >= '2014.01.01' 
AND congestion.date <= '2014.12.31' 
ORDER BY id_element, date 

Answer 2

Я считаю, что самый простой способ для использования подзапроса/CTE и условной агрегации:

SELECT c.date, c.week_nb, c.id_congestion, c.id_element, 
     ROW_NUMBER() OVER (PARTITION BY c.id_element ORDER BY c.date), 
     (CASE WHEN seqnum = 1 THEN 1 ELSE 0 END) as week_count 
FROM (SELECT c.*, 
      ROW_NUMBER() OVER (PARTITION BY c.congestion.id_element, c.week_nb 
           ORDER BY c.date) as seqnum 
     FROM congestion c 
    ) c 
WHERE c.date >= '2014.01.01' AND c.date <= '2014.12.31' 
ORDER BY id_element, date