MySQL通过Group By选择最大出现次数

Question

I have a table (log_entries):

id|token|area|
 1| 543 | AA |
 2| 452 | BB |
 3| 543 | BB |
 4| 634 | CC |
 5| 436 | AA |

I want to create a list of the top 5 areas, grouped by token, however the area used is the last area that token used. Basically a list of the top 5 areas where each token only gets one vote and it's vote is for the last area it was logged with.

For example, for the table above, the list would look like:

|area|count|
| BB |  2  |
| AA |  1  |
| CC |  1  |

How do I do this in a MySQL statement? (BTW the table is large > 50,000 rows)

Answer 1

SQL tables represent unordered sets. You need another column to specify the ordering.

Here is one way to get the most recent area for each token:

select area, count(*)
from (select t.*,
             (@rn := if(@t = token, @rn + 1,
                        if(@t := token, 1, 1)
                       )
             ) as seqnum
      from t cross join
           (select @rn := 0, @t := '') params
      order by tokens, ??
     ) t
where seqnum = 1
group by area
order by count(*) desc;

You need to replace the ?? with the column name that specifies the ordering to determine the most recent.