MySQL每天按类别分类的计数

Question

我有三张桌子。

categories表

id | 名称

items表

id | 名称| category_id

orders表

id | item_id | date_time | 交易代码

现在如何在查询中每天为每个类别选择具有特定交易代码的总订单。

所需结果：

Date        Category Total
2013-12-01  001      6
2013-12-01  002      0
2013-12-01  003      1
2013-12-02  001      14
2013-12-02  002      2
2013-12-02  003      0
2013-12-03  001      11
2013-12-03  002      4
2013-12-03  003      4

什么是编写此查询的最有效方法。

这是我到目前为止尝试过的：

SELECT DATE(od.trans_date) AS Date, ct.number AS Category, COUNT(od.id) AS Total 
from orders od
JOIN items im ON od.item_id = im.id
JOIN categories ct ON im.category_id = ct.id
WHERE od.trans_date BETWEEN '2013-12-01 00:00:00' AND '2013-12-03 23:59:59'
AND (od.transaction_code = 17 OR od.transaction_code = 15)
GROUP BY DATE(od.trans_date), ct.number ASC;

谢谢

Answer 1

我建议将您的JOINS更改为LEFT JOINS以便您的结果将包括没有任何项目的订单...

SELECT DATE(od.trans_date) AS Date, ct.number AS Category, COUNT(od.id) AS Total 
from orders od
LEFT JOIN items im ON od.item_id = im.id
LEFT JOIN categories ct ON im.category_id = ct.id
WHERE od.trans_date BETWEEN '2013-12-01 00:00:00' AND '2013-12-03 23:59:59'
AND (od.transaction_code = 17 OR tr.transaction_code = 15)
GROUP BY DATE(od.trans_date), ct.number ASC;

另外，您可能需要切换JOINS的顺序，以便显示所有类别，而不是所有顺序。

SELECT DATE(od.trans_date) AS Date, ct.number AS Category, COUNT(od.id) AS Total 
FROM categories ct
LEFT JOIN items im ON ct.id = im.category_id
LEFT JOIN orders od ON im.id = od.item_id
WHERE od.trans_date BETWEEN '2013-12-01 00:00:00' AND '2013-12-03 23:59:59'
AND (od.transaction_code = 17 OR tr.transaction_code = 15)
GROUP BY DATE(od.trans_date), ct.number ASC;