使用 MySQL 选择不存在的数据
我正在尝试选择两个日期范围之间的数据.但是，并非每天都会插入所有数据.以下是表格示例:
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)
场景是我想从 2012-07-02 到 2012-07-04 获得总出勤率.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?我确实研究了临时表.但是还是无法达到目的.
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
这是一个简单的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.
然后使用这个表左边的一个LEFT OUTER JOIN
Then use this table on the left of a 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 中的一个关键字，我在这里使用它是为了便于阅读.使用不同的列名.
DATE is a keyword in MySQL, I have used it here for readability. Use a different column name.
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