generate_series（）在PostgreSQL中按預期不能按預期方式工作

Question

我有一些稱爲分類的表，其中包含classification_indicator_id。
我需要總結這個ID並放入1天系列。
我需要添加大約20列（與另一個classification_indicator_id）。
我修改了一下回答previous question：

select 
data.d::date as "data", 
sum(c.classification_indicator_id)::integer as "Segment1", 
sum(c4.classification_indicator_id)::integer as "Segment2", 
sum(c5.classification_indicator_id)::integer as "Segment3" 
from 
    generate_series(
    '2013-03-25'::timestamp without time zone, 
    '2013-04-01'::timestamp without time zone, 
    '1 day'::interval 
) data(d) 
left join classifications c on (data.d::date = c.created::date and c.classification_indicator_id = 3) 
left join classifications c4 on (data.d::date = c4.created::date and c4.classification_indicator_id = 4) 
left join classifications c5 on (data.d::date = c5.created::date and c5.classification_indicator_id = 5) 
group by "data" 
ORDER BY "data" 

但仍然無法正常工作。 sum對於每一行都是很大的，而且我增加了額外的列。在與4列segment1爲2013年3月26日第二個表應該像第一張表等

With 3 column      With 4 columns 
data  | Segment1 | Segment2 data  | Segment1 | Segment2 | Segment3 
-------------------------------- ------------------------------------------- 
2013-03-25 | 12  | 16   2013-03-25 | 12  | 16  | 20 
-------------------------------- ------------------------------------------- 
2013-03-26 | 18  | 24   2013-03-26 | 108  | 144  | 180  

Answer 1

由於commented under your previous answer，你正在運行到「代理交叉連接」相同的金額。
我在這個相關的答案解釋的比較詳細：
Two SQL LEFT JOINS produce incorrect result

您的查詢應該像這樣工作：

SELECT d.created AS data 
     ,c3.segment1 
     ,c4.segment2 
     ,c5.segment3 
FROM (
    SELECT generate_series('2013-03-25'::date 
         ,'2013-04-01'::date 
         ,interval '1 day')::date AS created 
    ) d 
LEFT JOIN (
    SELECT created 
      ,sum(classification_indicator_id)::integer AS segment1 
    FROM classifications 
    WHERE classification_indicator_id = 3 
    GROUP BY 1 
    ) c3 USING (created) 
LEFT JOIN (
    SELECT created 
      ,sum(classification_indicator_id)::integer AS segment2 
    FROM classifications 
    WHERE classification_indicator_id = 4 
    GROUP BY 1 
    ) c4 USING (created) 
LEFT JOIN (
    SELECT created 
      ,sum(classification_indicator_id)::integer AS segment3 
    FROM classifications 
    WHERE classification_indicator_id = 5 
    GROUP BY 1 
    ) c5 USING (created) 
ORDER BY 1; 

假設created是date，而不是一個timestamp。

或者，甚至更快的查詢，因爲這已經成爲一個話題：

SELECT d.created AS data 
     ,count(classification_indicator_id = 3 OR NULL)::int * 3 AS segment1 
     ,count(classification_indicator_id = 4 OR NULL)::int * 4 AS segment2 
     ,count(classification_indicator_id = 5 OR NULL)::int * 5 AS segment3 
FROM (
    SELECT generate_series('2013-03-25'::date 
         ,'2013-04-01'::date 
         ,interval '1 day')::date AS created 
    ) d 
LEFT JOIN classifications c USING (created) 
GROUP BY 1 
ORDER BY 1; 

Answer 2

無需連接：

select 
    data.d::date as "data", 
    sum((classification_indicator_id = 3)::integer * classification_indicator_id)::integer as "Segment1", 
    sum((classification_indicator_id = 4)::integer * classification_indicator_id)::integer as "Segment2", 
    sum((classification_indicator_id = 5)::integer * classification_indicator_id)::integer as "Segment3", 
from 
    generate_series(
     '2013-03-25'::timestamp without time zone, 
     '2013-04-01'::timestamp without time zone, 
     '1 day'::interval 
    ) data(d) 
    left join 
    classifications c on data.d::date = c.created::date 
group by "data" 
ORDER BY "data"