mysql查询分组/按计数排序

Question

Here is a table:

ID    Item  status  updatetime   author
1     a     1       2014-01-02   Mike
2     a     1       2014-02-01   Jack
3     b     2       2014-01-10   John
4     b     1       2014-10-10   Ben
5     b     2       2014-01-11   Sam
6     c     3       2014-01-02   Aron
7     c     1       2014-11-01   Aron
8     c     1       2014-10-20   Max
9     d     3       2014-10-20   Mike

I would like to count the total number of each status for each Item, and the latest date/author of the items

The result should be like this:

count(status) =2 when item=a and status=1

count(status) =0 when item=a and status=2

count(status) =0 when item=a and status=3

Item    status_1    status_2    status_3    Latestupdate    author
a        2            0           0         2014-02-01       Jack
b        1            2           0         2014-10-10       Ben
c        2            0           1         2014-11-01       Aron
d        0            0           1         2014-10-20       Mike

How to write the sql ？

Answer 1

You want to do a pivot along with some other information. I would suggest this approach:

select item,
       sum(status = 1) as status_1,
       sum(status = 2) as status_2,
       sum(status = 3) as status_3,
       max(updatetime) as LatestUpdate,
       substring_index(group_concat(author order by updatetime desc), ',', 1) as author
from table t
group by item;

The tricky part is the last column, author . This uses a trick to get the author for the last update. The trick is to concatenate all the authors together, ordered by the update time. Then choose the first element of the list.