oracle - SQL average by customer per month -

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the table 'transactions' list of transactions date, customerid, cost per unit (price) , quantity.

i need report groups transactions months , gives count, total income , average income per customer.

i'm having trouble figuring out how insert group customerid select statement:

select extract(month date) month,        count(*) purchases,        sum(price*quantity) income,        avg(sum(price*quantity)) <-- needs grouped customerid aswell month     transactions     date between i2 , i3 group extract(month date);

the closest can like:

select extract(month date) month,        count(*) purchases,        sum(price*quantity) income,        ( select avg(sum(price*quantity))          transactions          group customerid, extract(month date) )     transactions t     date between i2 , i3 group extract(month date);

but approach stops making sense after think minute since nested select return multiple rows. , if add where clause , remove group date in second select:

(select avg(sum(price*quantity))  transactions  group customerid  extract(month date) = month)

then return... i'm not sure what, wrong.

it's oracle database way (10g think).

you can using arithmetic . . . divide total number of customers:

select extract(month date) month,        count(*) purchases,        sum(price*quantity) income,        sum(price*quantity) / count(distinct customerid)     transactions     date between i2 , i3 group extract(month date);

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