oracle - SQL to find the average amount of money spent by country? -


i need find average amount of money spent country, using 2 tables below in oracle. sale_total money spent in each sale , cust_country customer's country. appreciated.

tables

sale

 sale_id payment_id ship_id customer_id sale_total ==> money spent sale_date sale_time

customer

 cust_name cust_address cust_city cust_country cust_phone cust_age cust_sex

you need have link between sale , customer tables. presumably place customer_id in customer table primary key, , have customer_id in sale table foreign key. assuming that, can run below query.

select avg(s.sale_total) spent, c.cust_country sale s inner join customer c on s.customer_id=c.customer_id group c.cust_country

this tells average amount spent, , country spent.

the key understanding answer avg (the average function) aggregate function, combines things. when have aggregate function, have group other columns, hence why included group by clause.

the reason need customer id in customer table (apart being logical place it) can establish relationship between customer , sale tables.

another way establish relation can create new table link customer , sale together. call customer sales. example:

customer_sales

customer_id sale_id

then you'd adjust query join based on that.


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