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POsql select top 5 every month
 

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    <p>I have a mysql table of the format, let's call it product_revenue Product_id, year, month, revenue</p> <p>and i need to get the following columns: year, month, revenue_top_5_monthly</p> <p>where revenue_top_5_monthly is the sum of revenue of the products that had the highest revenue in that month. The top 5 products vary from month to month.</p> <p>I can do this for a single month by selecting with a sub-query a single month, sorting by revenue and using limit 5, then summing up the value, but I wouldn't know how to do this for every month in a single query</p> <p>What I have is</p> <pre><code>select 'y' as year, 'x' as month, sum(revenue) as revenue_top_5 from (select revenue from product_revenue where month=x and year=y order by revenue desc limit 5) as top5 </code></pre> <p>but I need it for every month in one shot.</p> <p>The product_revenue table has over 10m rows for 16 months, so final query speed is of large relevance. For one month it currently takes about 80-100 sec, and I have to run about 30 such queries, each for the whole 16 months, in a 1h 30min slot.</p> <p>as suggested, I also tried</p> <pre><code>select * from ( select dd.year, dd.monthnumber, u.product_id, sum(revenue) as revenue from source group by 1,2,3 )a where (select count(*) from (select dd.year, dd.monthnumber, u.product_id, sum(revenue) as revenue from source group by 1,2,3)b where b.year=a.year and b.monthnumber=a.monthnumber and b.revenue&lt;=a.revenue )&lt;=5 </code></pre> <p>but returns no rows. The individual subqueries a and b return the expected rows as named.</p>
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    1. COSounds like you need a composite index on `(year, month)`
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    2. COit's coming from a date dimension table, separate indexes vs composite index would only affect performance, not output number of rows, right?
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