Question

I have a problem to calculate easily some simple average. My table :

id / user / action     / data
1  / a    / unit_price / 40
2  / a    / quantity   / 1
3  / b    / unit_price / 70
4  / b    / quantity   / 2

Unit_price is a price for a user and quantity is quantity. So there i should get :
(40 + 70 + 70) / 3 = 60

If i do an

(AVG(action) WHERE action = unit_price)

I get :

(70+40)/2 = 55

If I do an

(SUM(action) WHERE action = unit_price) / (SUM(action) WHERE action = quantity)

I get :

110 / 3 = 36.6

The easiest way I found is to don’t put the unit_price but the global price then make a division in the PHP code to get the unit_price, but I was hoping SQL could do something for me.

Answer 1

select coalesce(sum(quantity * unit_price) /sum(quantity), 0) from
(select 
   sum(case when action='unit_price' then data else 0 end) as unit_price,
   sum(case when action='quantity' then data else 0 end) as quantity 
 from test
group by user) as a

SqlFiddle