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Ranking via variables

MySql MySql tricks

ranking.sql Raw #

set @type := '', @num := 1;

select type, variety, price, row_number
from (
   select type, variety, price,
       @num := if(@type = type, @num + 1, 1) as row_number,
       @type := type as dummy
   from fruits
) as x
where row_number <= 2;

+--------+----------+-------+------------+
| type   | variety  | price | row_number |
+--------+----------+-------+------------+
| apple  | gala     |  2.79 |          1 | 
| apple  | fuji     |  0.24 |          2 | 
| orange | valencia |  3.59 |          1 | 
| orange | navel    |  9.36 |          2 | 
| pear   | bradford |  6.05 |          1 | 
| pear   | bartlett |  2.14 |          2 | 
| cherry | bing     |  2.55 |          1 | 
| cherry | chelan   |  6.33 |          2 | 
+--------+----------+-------+------------+

ranking-left-join.sql Raw #

create table fruits (
    type varchar(10) not null,
    variety varchar(20) not null,
    primary key(type, variety));

insert into fruits values
('apple', 'gala'),
('apple', 'fuji'),
('apple', 'limbertwig'),
('orange', 'valencia'),
('orange', 'navel'),
('pear', 'bradford'),
('pear', 'bartlett'),
('cherry', 'bing'),
('cherry', 'chelan');

select l.type, l.variety, count(*) as num
from fruits as l
left outer join fruits as r
    on l.type = r.type
    and l.variety >= r.variety
group by l.type, l.variety;

+--------+------------+-----+
| type   | variety    | num |
+--------+------------+-----+
| apple  | fuji       |   1 |
| apple  | gala       |   2 |
| apple  | limbertwig |   3 |
| cherry | bing       |   1 |
| cherry | chelan     |   2 |
| orange | navel      |   1 |
| orange | valencia   |   2 |
| pear   | bartlett   |   1 |
| pear   | bradford   |   2 |
+--------+------------+-----+