mysql - 对子查询结果求和

Question

表示例:

| date_time           | quantity
-------------------------
| 2017-08-12 09:11:51 | 1
| 2017-08-12 10:12:51 | 1
| 2017-08-12 12:45:51 | 1
| 2017-08-13 11:12:51 | 1
| 2017-08-13 11:12:51 | 1
| 2017-08-13 12:45:51 | 1
| 2017-08-13 13:57:51 | 1
| 2017-08-14 14:23:51 | 1
| 2017-08-14 16:34:51 | 1
| 2017-08-15 16:21:51 | 1
| 2017-08-16 14:31:51 | 1

我可以通过以下查询获得结果:

SELECT DATE(date_time) as date_time
    ,SUM(quantity) as quantity
FROM report
WHERE date_time BETWEEN '' AND  ''
GROUP BY DATE(date_time)
HAVING SUM(quantity) < 3 

结果:

| date_time  | quantity
 -------------
| 2017-08-14 | 2
| 2017-08-15 | 1
| 2017-08-16 | 1

我想之后对数量进行求和。例如:

 quantity
---------
| 4

为了实现这一目标，我知道我需要使用结果作为子查询来求和。我尝试了这个，但它是错误的:

SELECT SUM(topla) FROM (
  ( SELECT DATE(date_time) as date_time
        ,SUM(quantity) as quantity
    FROM report
    WHERE date_time BETWEEN '' AND  ''
    GROUP BY DATE(date_time)
    HAVING SUM(quantity) < 3 
  ) AS topla
)

如何对数量求和？

Answer 1

首先，您必须按列名称对数量求和。 (在示例中我将其命名为 sub_quantity)

其次，您不需要选择日期。

所以你的查询可能是

SELECT SUM(sub_quantity) AS quantity
FROM
  ( SELECT SUM(quantity) AS sub_quantity
   FROM report
   WHERE date_time BETWEEN '' AND ''
   GROUP BY DATE(date_time)
   HAVING SUM(quantity) < 3) a