表连接oracle sql中的顺序

Question

您是否可以就表格的正确加入顺序提供建议，即4个表格合并我们必须考虑的订单数据。由于我在运行查询时遇到问题，因此出现ORA-00904错误：

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

您要加入profits表两次，而不是加入products表。看起来你的意思是：

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将决定加入顺序，但在您加入表之前，您无法引用该表。