使用MySQL选择不存在的数据 [英] Selecting Non-existent Data With MySQL

问题描述

我正在尝试选择两个日期范围之间的数据.但是，并非每天都插入所有数据.下面是该表的示例:

I'm trying to select data between two date range. However not all data are being inserted daily. Below is sample of the table:

mysql> SELECT * FROM attendance;
+------------+-------+
| date       | total |
+------------+-------+
| 2012-07-02 |   100 |
| 2012-07-04 |    70 |
| 2012-07-05 |    78 |
+------------+-------+
3 rows in set (0.00 sec)

这种情况是，我希望从2012-07-02到2012-07-04总共能出席.根据上面的数据，我会得到

The scenario is I want to get total of attendance from 2012-07-02 till 2012-07-04. Based on the data above I will get

mysql> SELECT * FROM attendance WHERE date BETWEEN '2012-07-02' AND '2012-07-04';
+------------+-------+
| date       | total |
+------------+-------+
| 2012-07-02 |   100 |
| 2012-07-04 |    70 |
+------------+-------+
2 rows in set (0.00 sec)

但是我的目标是将2012-07-03包含在结果中.

However my objective is to have 2012-07-03 included in the result.

+------------+-------+
| date       | total |
+------------+-------+
| 2012-07-02 |   100 |
| 2012-07-03 |     0 |
| 2012-07-04 |    70 |
+------------+-------+

这可以通过MySQL完成吗?我确实查看了临时表.但仍然无法实现目标.

Is this possible to be done through MySQL? I did look into temporary table. But still unable to achieve the objective.

推荐答案

这是使用简单解决方案的常见问题.

This is a common problem with a simple solution.

创建一个常规表(例如REF_DATE)，并将所有日期存储在其中，例如3年或您需要的任何时间跨度.

Create a regular table, say REF_DATE, and store in it all dates for like 3 years or whatever time span you would need.

然后在LEFT OUTER JOIN

SELECT REF.date,IFNULL(A.total,0) as total FROM REF_DATE REF 
LEFT OUTER JOIN attendance 
ON REF.date=A.date
A WHERE REF.date BETWEEN '2012-07-02' AND '2012-07-04';

DATE是MySQL中的关键字，出于可读性考虑，我在这里使用了它.使用其他列名称.

DATE is a keyword in MySQL, I have used it here for readability. Use a different column name.

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