Oracle SQL中的表连接顺序

Question

Could you give advice on correct joining order for tables ie for 4 tables combining data which order we have to take into consideration. As I am having problems in running queries and I am getting an ORA-00904 error:

select countries.country_name, profits.amount_sold, products.prod_name
from countries
join customers on countries.country_id = customers.country_id
join profits on products.prod_id = profits.prod_id
join profits on profits.cust_id = customers.cust_id
WHERE COUNTRY_NAME = 'India'

Answer 1

You are joining to the profits table twice, and not joining to the products table. Looks like you meant it to be:

select countries.country_name, profits.amount_sold, products.prod_name
from countries
join customers on countries.country_id = customers.country_id
join profits on profits.cust_id = customers.cust_id
join products on products.prod_id = profits.prod_id
WHERE COUNTRY_NAME = 'India'

Oracle will decide the join order, but you can't reference a table before you've joined to it.