如何返回給定月份的連接記錄數？

我有以下簡單的模式：如何返回給定月份的連接記錄數？

CREATE TABLE POSTS (
    ID INT NOT NULL, 
    DATE  DATE NOT NULL, 
    [Other stuff omitted] 
); 

CREATE TABLE TOPICS (
    ID INT NOT NULL, 
    [Other stuff omitted] 
); 

CREATE TABLE THETA (
    POST_ID INT NOT NULL, 
    TOPIC_ID INT NOT NULL, 
    WEIGHT FLOAT NOT NULL 
);

我有一個查詢到所有崗位總和的重量在THETA，按日期和主題ID分組：

SELECT THETA.TOPIC_ID as TopicID, POSTS.DATE as Date, SUM(THETA.WEIGHT) as Value 
    FROM POSTS INNER JOIN THETA 
    WHERE THETA.POST_ID=POSTS.ID 
    GROUP BY YEAR(POSTS.DATE), MONTH(POSTS.DATE), TopicID;

可正常工作，給結果是這樣的：

+---------+------------+---------------------+ 
| TopicID | Date  | Value    | 
+---------+------------+---------------------+ 
|  0 | 2008-08-19 | 350.4930010139942 | 
|  0 | 2008-09-18 | 1745.5010008439422 | 
|  0 | 2008-10-03 | 1468.824001269415 | 
|  0 | 2008-11-25 | 1079.579000659287 | 
|  0 | 2008-12-11 | 1070.3860008455813 | 
|  0 | 2009-01-24 | 1453.3730010837317 | 
|  0 | 2009-02-20 | 1139.2920009773225 | 
|  1 | 2008-08-19 | 288.09700035490096 | 
|  1 | 2008-09-22 | 1307.5790000930429 | 
|  1 | 2008-10-16 | 1050.1739999558777 | 
|  1 | 2008-11-11 | 868.2280002105981 | 
|  1 | 2008-12-18 | 897.6830000579357 | 
|  1 | 2009-01-12 | 1148.5619999151677 | 
|  1 | 2009-02-12 | 858.0710002686828 | 
|  2 | 2008-08-19 | 415.83300026878715 | 
...

但是，我想通過該月的帖子數規範化價值。例如，如果月份2008-08-19中有100個帖子，則第一個結果行的值爲3.50493，八個結果行的值爲2.88097。面臨的挑戰是每月的帖子數量不盡相同，所以我不太確定該怎麼做。有任何想法嗎？

來源

2013-09-25 stepthom

也許：

SELECT t.TOPIC_ID as TopicID, p.DATE as Date, SUM(t.WEIGHT)/s.Month_CT as Value 
FROM POSTS p 
JOIN THETA t 
    ON t.POST_ID = p.ID 
JOIN (SELECT YEAR(DATE) as Yr, MONTH(DATE) as Mnth, COUNT(ID) as Month_CT 
     FROM POSTS 
     GROUP BY YEAR(DATE), MONTH(DATE) 
     )s 
    ON YEAR(p.DATE) = s.Yr 
    AND MONTH(p.DATE) = s.Mnth 
GROUP BY YEAR(p.DATE), MONTH(p.DATE), TopicID;

來源

2013-09-25 19:39:20

這將由每人每月主題無關的帖子正常化，而不是每月的所有帖子 – Quassnoi

@Quassnoi感謝，misssed的TopicID在'GROUP BY'更新。 –

@GoatCO。謝謝你。我試了一下，得到以下錯誤：「錯誤1054（42S22）：'字段列表'」中的'THETA.TOPIC_ID'列未知。 – stepthom

SELECT t.topic_id TopicID, 
     CONCAT(y, '-', m, '-01') AS Date 
     SUM(t.weight)/cnt as NormalizedValue 
FROM (
     SELECT YEAR(date) y, 
       MONTH(date) m, 
       COUNT(*) AS cnt 
     FROM posts 
     GROUP BY 
       y, m, cnt 
     ) p 
JOIN posts p 
ON  p.date >= '0000-01-01' + INTERVAL y YEAR + INTERVAL m - 1 MONTH 
     AND p.date < '0000-01-01' + INTERVAL y YEAR + INTERVAL m MONTH 
JOIN theta t 
ON  t.post_id = p.id 
GROUP BY 
     y, m, t.topic_id

來源

2013-09-25 20:01:05 Quassnoi

如何返回給定月份的連接記錄數？

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