Question

I couldn’t figure out how to optimize this query and I didn’t find a similar query as example.

What would be the best way to rewrite this query in order not to have so many sub-queries in the select clause achieving the same result grouped by month/brand_id?

The DBMS is SQL Server.

select
    o.brand_id,
    count(o.item_id) as "Total bought items",
    count(o.sell_date) as "Total sold items",
     /* Amount of sold items grouped by month per item */
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 1 and obj.brand_id = b.brand_id) as "Jan",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 2 and obj.brand_id = b.brand_id) as "Feb",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 3 and obj.brand_id = b.brand_id) as "Mar",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 4 and obj.brand_id = b.brand_id) as "Apr",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 5 and obj.brand_id = b.brand_id) as "May",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 6 and obj.brand_id = b.brand_id) as "Jun",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 7 and obj.brand_id = b.brand_id) as "Jul",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 8 and obj.brand_id = b.brand_id) as "Aug",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 9 and obj.brand_id = b.brand_id) as "Sep",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 10 and obj.brand_id = b.brand_id) as "Oct",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 11 and obj.brand_id = b.brand_id) as "Nov",
    (select count(obj.sell_date) from tab_object as obj where month(obj.install_date) = 12 and obj.brand_id = b.brand_id) as "Dec"
from  tab_brand as b
left join tab_object as o on b.brand_id = o.brand_id
                            and year(o.sell_date) = 2012
where b.brand_id in (1234, 1324, 1423, 2314)
group by b.brand_id
order by b.brand_id;

Answer 1

You’re looking for a PIVOT http://msdn.microsoft.com/en-us/library/ms177410(v=sql.105).aspx and join the results of that to a query to provide the totals

select TotalBought, TotalSold, months.* from
(
select 
    o.brand_id,
    count(o.item_id) as TotalBought, 
    count(o.sell_date) as TotalSold
from tab_object o   
where year(sell_date)=2012
group by brand_id
) totals
    left join
(    
select * 
  from (select brand_id, sell_date, left(datename(month,install_date),3) as InstallMonth 
        from tab_object where brand_id in (1234,1324,1423,2314) and year(sell_date)=2012
  ) src 
  pivot 
  ( count(sell_date) for installmonth in ([Jan],[Feb],[Mar],[Apr],[May],[Jun],[Jul],[Aug],[Sep],[Oct],[Nov],[Dec])) p
) months
    on totals.brand_id = months.brand_id

You don’t seem to use the brand table either