douchenbiao0916 2014-10-17 12:57
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在MySQL中使用条件语句定义变量

I have a table "products" with columns like:

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

*start_discount and end_discount is a UNIX timestamp

Current price of a product depends on time - if 'time()' is between 'start_discount' and 'end_discount' then the current price is 'discount_price', otherwise is 'price'

I am trying to return "current_price" variable. In PHP, I would just write:

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

How can I achieve the same as above in MySQL without involving PHP?

I have this so far:

SELECT *, (**price OR discount_price**) as current_price FROM products WHERE active = 1 AND current_price BETWEEN '100' AND '200' ORDER BY current_price;
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  • donglin6659 2014-10-17 13:10
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    Here is a way to do it, I am only selecting the price you can select whatever you want from the table

    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
    

    EDIT : Just noticed you are using current_price in the where condition, which you can not do since its an alias so you may need to use a table column in the where clause or use having clause as

    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
    

    Here is a test I did

    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)
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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