你可以在不同的列上分组和计算mysql吗？

Question

Users have a list with items in different categories. I want to know how many items a user has in each category.

User    |   item  | category
____________________________
Bill    |   car   | new
Bill    |   truck | used
Bill    |   boat  | new
Bill    |   house | old
Sue     |   car   | used
Sue     |   truck | used
Bill    |   bike  | new
Sue     |   viola | used

I'd like the results

User category
__________________________
Bill|  new   |  3
Bill|  used  |  1
Bill|  sold  |  1

I've tried

$SQL = "SELECT COUNT(DISTINCT CATEGORY) FROM LIST WHERE USER=Bill";

but it doesn't get me very far.

Thanks

Answer 1

You need to use group by statement:

select user, category, count(distinct item)
from mytable
where user = 'Bill'
group by user, category