加入内部和外部子查询

Question

我正在处理 3 table 的销售、客户和产品，我想从销售 table 和 customer_name 中获取所有列，客户年龄来自客户 [=17] =] 和 product_name，来自同一结果集中产品 table 的类别。有一个条件，我必须使用 2 个连接操作，其中一个连接将在子查询内部，另一个在子查询外部。这是我的查询不起作用：

 SELECT a.*,
    b.customer_name,
    b.age, 
    b.customer_id 
 FROM sales AS a
 LEFT JOIN customer AS b on a.customer_id = b.customer_id
 LEFT JOIN (SELECT product_id, product_name, category from product) as c
    ON a.product_id = c.product_id
 ORDER BY a.customer_id, b.customer_id;

只有第一个连接在这个查询中起作用。

Answer 1

select 
a.*,
b.customer_name,
b.age, 
b.customer_id ,
c.*
from sales as a
left join customer as b
on a.customer_id = b.customer_id
LEFT JOIN (SELECT product_id, product_name, category from product) as c
ON a.product_id = c.product_id
order by a.customer_id;

https://www.db-fiddle.com/f/wKbMaD6UF1v3a4KCXE7248/0

加入内部和外部子查询

Join in inside and outside subquery

sql

join

subquery