Question

我需要计算一些列中出现的几个类别的次数。它们像Sports，Medicine这样的字符串，列名是ct.category_name。

这是我正在调整的查询。我希望每个类别的列都有一个列。

select co.order_id, co.catalog_item_id, ct.category_name               
from customer_order as co
join item_category as ic on (ic.item_id = co.customer_id )
join category_translations as ct on (ct.category_id = ic.category_id)
where co.paid = 1 and co.customer_id = 22500 and ct.locale = "en"

当我把它放在select语句中时它会计算一切，我明白为什么，但我不确定要走哪条路。

count(CASE 
    WHEN ct.category_name = "sports" THEN ct.category_name 
     ELSE 0 
    end) AS 'sports'

同样，我希望每个字符串的计数都是它自己的列。任何帮助将不胜感激。

当我尝试：

select co.order_id, co.catalog_item_id, ct.category_name
, SUM(ct.category_name = "sports") AS `sports`
, SUM(ct.category_name = "medici") AS `medicine`


from customer_order as co

join item_category as ic on (ic.item_id = co.customer_id )
join category_translations as ct on (ct.category_id = ic.category_id)


where co.paid = 1 and co.customer_id = 22500 and ct.locale = "en"

它算两次运动。错误的地方何时？结果：

`23115  271708  sports  483 483`

Answer 1

它会计算所有内容，因为COUNT会为每个非空值增加其值，而0不是NULL。

可能的解决方案：

将0替换为NULL或

使用SUM代替COUNT：

SUM(CASE 
WHEN ct.category_name = "sports" THEN 1
 ELSE 0 
end) AS 'sports'

甚至

SUM(ct.category_name = "sports") AS `sports`

mysql计数出现一个字符串

1 个答案: