MySQL Select 与左连接不同？

Question

我正在尝试获取 company_id 中没有公司级备注的列表。但是，该公司可能有位置级别的注释。

company
-------------------------
company_id  name  deleted
1           Foo   0
2           Bar   0
3           Baz   0

location
-----------------------
location_id  company_id
6            1
7            2
8            3

note
-----------------------------------------
note_id  company_id  location_id  deleted
10       2           6            0         // location-level note
11       1           7            0         // location-level note
12       null        8            0         // location-level note
13       2           null         0         // company-level note

我希望我的结果 table 是这样的：

company_id  name
1           Foo
3           Baz

更新

Foo/company_id = 1 没有公司级别的备注，因为该备注也有 location_id，这使其成为位置级别的备注。公司级别的注释是仅 link 给公司（而不是地点）的注释。

更新结束

我试过这样做，但它 returns 是一个空集，所以我不确定它是否有效，而且没有任何公司没有公司级别的注释，或者我是否'我做错事了。

SELECT DISTINCT 
c.company_id, 
c.name
FROM company AS c
LEFT JOIN note AS n
ON c.company_id = n.company_id
WHERE 
c.deleted = 0 AND
n.deleted = 0 AND
n.location_id IS NOT NULL AND 
n.location_id != 0 AND
c.company_id = (SELECT MAX(company_id) FROM company)

Mike 修改后的已接受答案

SELECT
    company_id,
    name
FROM company
WHERE 
    deleted = 0 AND
    company_id NOT IN (
        SELECT DISTINCT 
            c.company_id
        FROM company AS c 
        INNER JOIN note AS n 
        ON c.company_id = n.company_id 
        WHERE (
            n.deleted = 0 AND
                (n.location_id IS NULL OR 
                n.location_id = 0)
        )
    );

Answer 1

考虑这个问题的最简单方法是首先找到所有具有公司级别注释的公司，您可以使用

 select distinct c.company_id
   from company c 
 inner join notes n 
     on c.company_id = n.company_id 
  where n.location_id is null;

然后只需将这些公司从公司select中删除：

select company_id,
       name
  from company
 where company_id not in (select distinct c.company_id
                            from company c 
                          inner join notes n 
                              on c.company_id = n.company_id 
                           where n.location_id is null);

*已更新为使用内部联接而不是逗号分隔联接。

Answer 2

SELECT DISTINCT c.* 
  FROM company c 
  LEFT 
  JOIN note n 
    ON n.company_id = c.company_id 
   AND n.location_id IS NULL 
 WHERE n.note_id IS NULL;

MySQL Select 与左连接不同？

MySQL Select Distinct with Left Join?

mysql

sql

select

distinct

left-join

Mike 修改后的已接受答案