php - mysql用循环计数行

Question

我有下表:

+-------------+--------------+ 
| product     | purchased    |
+-------------+--------------+ 
| Hammer      | <timestamp>  |
| Nipper      | <timestamp>  |
| Saw         | <timestamp>  |
| Nipper      | <timestamp>  |
| Hammer      | <timestamp>  |
| Hammer      | <timestamp>  |
| Saw         | <timestamp>  |
| Saw         | <timestamp>  |
| Saw         | <timestamp>  |
+-------------+--------------+

我想查看有关这些产品保修状态的摘要。保修期应为自购买之日起 5 年。因此，对于今天的日期，应该可以检查产品是否在保修期内(基于购买日期)。另外，我现在想知道最后一次购买的产品何时会超出保修范围。这是一个示例表:

+-------------+--------------+----------------+------------------+------------------+
| product     | count        | warranty valid | warranty expired | last p. warranty |
+-------------+--------------+----------------+------------------+------------------+
| Hammer      | 3            | 1              | 2                | 10.03.2015       |
| Nipper      | 2            | 2              | -                | 01.01.2014       |
| Saw         | 4            | 1              | 3                | 02.12.2013       |
+-------------+--------------+----------------+------------------+------------------+

我试图为这个例子创建查询，但我不知道如何循环每个产品的结果来计算有效保修等。这就是我现在所拥有的:

SELECT
    product,
    date_format(from_unixtime(purchased), '%d.%m.%Y') AS purchaseDate,
    date_format(date_add(from_unixtime(purchased), INTERVAL 5 YEAR), '%d.%m.%Y') AS warrantyEnd,
    (
        SELECT
            COUNT(product)
        FROM
            productWarranty
    ) AS count
FROM
    productWarranty s
GROUP BY
    product

我不知道如何编写子查询，因为我需要使用类似 WHERE product = Hammer 的东西。但是我怎样才能让 sql 为每个产品循环呢？

Answer 1

您需要处理的是保修是否仍然有效或已过期以及保修日期，因此您首先需要构建一个表来反射(reflect)这一点:

select   product
       , IF( warranty >= NOW(), 1, 0 ) as valid
       , IF( warranty < NOW(), 1, 0 ) as expired
       , warranty as last
from     (
           select   product
                ,   ADDDATE( purchased, INTERVAL 5 YEAR ) as warranty
           from     productWarranty
         ) w
group by product
;

那会让你得到类似的东西:

+---------+-------+---------+---------------------+
| product | valid | expired | warranty            |
+---------+-------+---------+---------------------+
| Hammer  |     1 |       0 | 2017-01-01 00:00:00 |
| Nipper  |     1 |       0 | 2017-01-01 00:00:00 |
| Nipper  |     1 |       0 | 2017-01-01 00:00:00 |
| Nipper  |     1 |       0 | 2017-01-01 00:00:00 |
| Saw     |     1 |       0 | 2017-01-01 00:00:00 |
| Saw     |     0 |       1 | 2011-01-01 00:00:00 |
| Saw     |     1 |       0 | 2017-01-01 00:00:00 |
| Saw     |     1 |       0 | 2017-01-01 00:00:00 |
+---------+-------+---------+---------------------+

然后使用聚合函数过滤和汇总您要查找的信息:

select   product
       , SUM( IF( warranty >= NOW(), 1, 0 ) ) as valid
       , SUM( IF( warranty < NOW(), 1, 0 ) ) as expired
       , MAX( warranty ) as last
from     (
           select   product
                  , adddate( purchased, interval 5 year ) as warranty
           from productWarranty
         ) w
group by product
;

+---------+-------+---------+---------------------+
| product | valid | expired | last                |
+---------+-------+---------+---------------------+
| Hammer  |     1 |       0 | 2017-01-01 00:00:00 |
| Nipper  |     3 |       0 | 2017-01-01 00:00:00 |
| Saw     |     3 |       1 | 2017-01-01 00:00:00 |
+---------+-------+---------+---------------------+