Question

SELECT *, 
       DATE(date) AS post_day 
FROM   notes 
WHERE  MONTH(date) = '08' 
       AND userid = '2' 
       AND YEAR(date) = '2016' 
ORDER  BY post_day DESC, 
          timestamp ASC

在这个查询中，我按天分组我的帖子。

我正在努力的是计算每天所有笔记的总字数。有一个单词计数列，其中包含每个帖子的单词计数。是否可以在同一查询中计算此总和，还是需要单独进行？

按表格列：

NoteID    UserID    Date    Note    WordCount

Answer 1

SELECT date, SUM(wordCount) AS monthWordCount
    FROM Notes
    WHERE userID = 2
    AND MONTH(date) = '08'
    AND YEAR(date) = '2016'
    GROUP BY userID, date

使用上面的代码查看此demo。

如果你想要返回笔记，你也可以做如下的子查询：

SELECT noteID, userID, date, note, wordCount, 
  (SELECT SUM(wordCount)
    FROM Notes
    WHERE userID = a.userID
    AND date = a.date
    GROUP BY userID) AS dayTotalWordCount
FROM Notes a
WHERE a.userID = 102
AND MONTH(date) = '08'
AND YEAR(date) = '2016'

这是使用上述代码的demo。

Answer 2

首先，不要将select *与group by查询一起使用。 select *对聚合没有意义。。。你需要应用聚合函数。

我认为你想要这样的东西：

SELECT DATE(date) as post_day, SUM(WordCount)
FROM notes
WHERE MONTH(date)= '08' AND userid = '2' AND YEAR(date)= '2016'
GROUP BY DATE(date)
ORDER BY post_day DESC, timestamp ASC

按天计算总和分组

2 个答案: