组合左外连接和内连接 + 聚合函数 - 空结果集问题

Question

这可能很简单，但我现在还没有看到。尝试组合左外连接和内连接，以便从给定的一组表中获取任何可用信息，所有信息都与 customer_id

相关

示例在设计上可能并不完美（我根据实际查询编造的），但足以说明我的问题，这是一个空结果集，即使其中一些表中有行.

示例表：

简介：

id_profile   nm_profile 
-----------  ----------  
1234         User profile

订单：

id_order id_customer order_date    order_type
-------  ----------  ---------     ----------     
10308    1234        2017-09-18    Online
10309    1234        2018-09-18    Online

评论：

   id_review  id_profile   id_order   text    score   
   ---------  ----------   --------   -----   ------
   (no rows for this id_profile)

查询：

SELECT c.id_customer, MIN(o.order_date) order_date, r.text review_text
FROM Customer c
JOIN Profile p ON c.id_customer = p.id_profile 
LEFT OUTER JOIN Orders o ON o.id_customer = c.id_customer AND o.order_type = 'Online'
LEFT OUTER JOIN Reviews r ON r.id_reviewer = p.id_profile AND r.score = 5
WHERE c.id_customer = 1234
GROUP BY c.id_customer

假设这些列匹配并且我能够运行上面的查询，我试图实现以下目标：

id_customer    order_date   review_text
-----------    ----------   -----------
1234           2017-09-18   <NULL>

这是一个更大查询的一部分；试图将其分解为最基本的表达方式，以了解我可能做错了什么。试图避免连接中的 WHERE 子句，也尝试了 LEFT OUTER JOIN (SELECT ....) ，但没有运气。

提前致谢！

Answer 1

聚合完成后您应该加入Reviews：

SELECT t.id_customer, t.order_date, r.text review_text
FROM ( 
  SELECT c.id_customer, MIN(o.order_date) order_date
  FROM Customer c
  INNER JOIN Profile p ON c.id_customer = p.id_profile 
  LEFT JOIN Orders o ON o.id_customer = c.id_customer AND o.order_type = 'Online'
  WHERE c.id_customer = 1234
  GROUP BY c.id_customer
) t
LEFT JOIN Reviews r ON r.id_reviewer = t.id_customer AND r.score = 5;

参见demo。

Answer 2

如果你只想要最大订单日期的所有评论信息，那么你可以总结 orders table 并加入其余的：

SELECT c.id_customer, o.min_order_date, r.text as review_text
FROM Customer c JOIN
     Profile p ON c.id_customer = p.id_profile LEFT JOIN
     (SELECT o.id_customer, MIN(o.order_date) as min_order_date
      FROM Orders o
      WHERE o.order_type = 'Online'
      GROUP BY o.id_customer
     ) o
     ON o.id_customer = c.id_customer LEFT JOIN 
     Reviews r
     ON r.id_reviewer = p.id_profile AND r.score = 5
WHERE c.id_customer = 1234;

如果 id_customer 有多个评论，这将 return 多行。你的问题没有提到如何处理。

组合左外连接和内连接 + 聚合函数 - 空结果集问题

Combining Left Outer and Inner Joins + Aggregate Function - Empty result set issue

sql

join

group-by

sybase

sybase-ase15