mysql - Limit results in join query -

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this question has answer here:

i have 2 tables: list of cities, , list of categories each city.

table tv_village  id    | name -------------- 1     | london 2     | paris   table tv_village_category  village_id | category   | total ----------------------------- 1          | event      | 10 1          | realestate | 15 1          | job        | 8 1          | place      | 20 2          | event      | 42 2          | realestate | 66 2          | job        | 83 2          | place      | 55

my question

i need top 3 categories each city (sort total).

what tried

when try query, tells me field v.id unknown subquery.

    select *     tv_village v     inner join (         select *         tv_village_category vc2         vc2.village_id = v.id             , vc2.total > 0         order vc2.total desc         limit 3     ) vc     order v.id, vc.total desc

i need add performances matters, , tables bit huge (36k cities , 1m categories).

regards,

one method try variables:

select v.* (select v.*,              (@rn := if(@v = village_id, @rn + 1,                         if(@v := village_id, 1, 1)                        )              ) seqnum       tv_village v cross join            (select @rn := 0, @v := '') params       order village, total desc      ) v seqnum <= 3;

this can take advantage of index on tv_village(village_id, total).


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