select
	product.id
	,detail.name
	,product.price
	-- 可以把区分code转换为名称
	, (SELECT testFild from country where country.id = product.id) AS testFild
	-- 当满足某些条件的时候才会进行查询
	,CASE
		WHEN product.price > 100 THEN
			(select country from country where country.id = product.id)
		ELSE '其他' 
	END country
from
	product
left JOIN 
	detail
ON
	product.id = detail.id