php - MySQL中使用条件语句定义变量

Question

我有一个表“产品”，其中包含以下列:

| price | discount_price | start_discount | end_discount | ... |

*start_discount 和 end_discount 是 UNIX 时间戳

产品的当前价格取决于时间 - 如果“time()”介于“start_discount”和“end_discount”之间，则当前价格为“discount_price”，否则为“price”

我正在尝试返回“current_price”变量。在 PHP 中，我会这样写:

$current_price = (time() > $start_discount && time() < $end_discount)? $discount_price : $price;

如何在不涉及 PHP 的情况下在 MySQL 中实现与上述相同的效果？

到目前为止我有这个:

SELECT *, (**price OR discount_price**) as current_price FROM products WHERE active = 1 AND current_price BETWEEN '100' AND '200' ORDER BY current_price;

Answer 1

这里有一个方法，我只是选择价格，你可以从表中选择你想要的任何内容

select
case when
 now() > start_discount AND now() < end_discount then discount_price
else price end as current_price
from 
products 
WHERE 
active = 1 
AND price BETWEEN '100' AND '200'
ORDER BY current_price

编辑:刚刚注意到您在 where 条件中使用 current_price ，但您不能这样做，因为它是别名，因此您可能需要在 where 子句中使用表列或使用 having子句为

select
case when
 now() > start_discount AND now() < end_discount then discount_price
else price end as current_price
from 
products 
WHERE 
active = 1 
having current_price BETWEEN '100' AND '200'
ORDER BY current_price

这是我做的测试

mysql> create table products (price int, discount_price int ,start_discount date ,end_discount date);
Query OK, 0 rows affected (0.08 sec)

mysql> insert into products values (100,60,'2014-10-01','2014-11-01'),(200,160,'2014-10-01','2014-10-10'),(300,200,'2014-11-01','2014-11-15');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select case when  now() > start_discount AND now() < end_discount then discount_price else price end as current_price from  products order by current_price;
+---------------+
| current_price |
+---------------+
|            60 |
|           200 |
|           300 |
+---------------+
3 rows in set (0.00 sec)