Question

Let’s say that we have a table with COLUMN1 and COLUMN 2. Here’s a sample of the records:

COLUMN 1 | COLUMN 2
124 | 12
124 | 11
124 | 10
124 | 9
26  | 8
65  | 7
65  | 6
65  | 5
65  | 4
23  | 3
124 | 2
124 | 1
124 | 0

There is absolutely no pattern to this, but what I’d like to do is get:

COUNT(*) | COLUMN 1 | Smallest Column 2
4 | 124 | 9
1 | 26  | 8
4 | 65  | 4
1 | 23  | 3
3 | 124 | 0

So far, I’ve been doing this with PHP, but I’d like to find a way to do this in MySQL, as I’m sure it’d be a lot more efficient. The problem is, I can’t even think of where to start with this. A regular GROUP BY COLUMN 1 wouldn’t work because I want two results for 124, since it appears in two different instances. I’ve been fiddling around for hours and looking into the documentation and Google, but I haven’t been able to find anything yet, and I was wondering if any of you would be able to point me in the right direction. Is this even possible with MySQL?

Answer 1

Well, it took a bit of fiddling, but here it is!

This assumes you have an id column in your table that you order by to get a consistent ordering (if you don’t have an id column, order by timestamp or whatever in the inner query).

set @prev := '', @low := 0, @cnt := 0, @grp :=0;
select cnt, column1, low
from (
    select
        column2, 
        @low := if(@prev = column1, least(column2, @low), column2) low,
        @cnt := if(@prev = column1, @cnt + 1, 1) cnt,
        @grp := if(@prev = column1, @grp, @grp + 1) grp,
        @prev := column1 column1
    from (select column1, column2 from so9091342 order by id) x
    order by grp, cnt desc) y
group by grp;

Here’s the sql needed to set up a table for testing:

create table so9091342 (id int primary key auto_increment, column1 int, column2 int);
insert into so9091342 (column1, column2) values (124,12),(124,11),(124,10),(124,9),(26,8),(65,7),(65,6),(65,5),(65,4),(23,3),(124,2),(124,1),(124,0);

Output of above query:

+------+---------+------+
| cnt  | column1 | low  |
+------+---------+------+
|    4 |     124 |    9 |
|    1 |      26 |    8 |
|    4 |      65 |    4 |
|    1 |      23 |    3 |
|    3 |     124 |    0 |
+------+---------+------+

p.s. I named the table so9091342 because this is SO question ID #9091342.