如何用 JOIN 替换 NOT EXISTS？

Question

我有以下查询：

select distinct a.id, a.name
from Employee a
join Dependencies b on a.id = b.eid
where not exists 
    ( 
select * 
    from Dependencies d 
    where b.id = d.id 
    and d.name  = 'Apple'
    )
and exists 
    (
    select * 
    from Dependencies c 
    where b.id = c.id 
    and c.name  = 'Orange'
    );

我有两张桌子，比较简单。 第一个 Employee 有一个 id 列和一个 name 列 第二个表 Dependencies 有 3 列，一个 id、一个 eid（要链接的员工 id）和名称（apple、orange 等）。

数据看起来像这样 员工表是这样的

id  | name
-----------
1   | Pat
2   | Tom
3   | Rob
4   | Sam

依赖关系

id  | eid | Name
--------------------
1   | 1   |  Orange
2   | 1   |  Apple
3   | 2   |  Strawberry
4   | 2   |  Apple
5   | 3   |  Orange
6   | 3   |  Banana

如您所见，Pat 同时拥有 Orange 和 Apple，他需要被排除在外，并且必须通过连接，而我似乎无法让它工作。最终数据应该只返回 Rob

Answer 1

inner join 用你想要的名字，left join 用你不想要的名字，然后用 where 确保 left join 不匹配，像这样（SQL Fiddle）：

select distinct a.id, a.name
from Employee a
  inner join Dependencies b on a.id = b.eid
    and b.name = 'Orange'
  left join Dependencies c on ( a.id = c.eid
    and c.name = 'Apple')
where c.id is null;

Answer 2

将需要两个连接到 Dependencies，因为有 2 个测试。暂时忽略性能，您可以尝试通过命名别名来提高连接的可理解性，例如：

SELECT DISTINCT e.ID, e.Name
   FROM Employee e
   LEFT OUTER JOIN Dependencies withApple
      ON withApple.eid = e.id
      AND withApple.Name = 'Apple'
   LEFT OUTER JOIN Dependencies withOrange
      ON withOrange.eid = e.id
      AND withOrange.Name = 'Orange'
   WHERE
      withApple.id IS NULL -- Don't want this
      AND
      withOrange.id IS NOT NULL -- Do want this.

SqlFiddle