Question

我有NighClub，Visitor和Visitors_NighClub表（很多）。 我需要获得所有没有某些访客的夜总会。

要让某些访客拥有NightClub，我喜欢这样：

id

但是如何让整夜没有一定访客的俱乐部。我不能喜欢：

link

Answer 1

您可以尝试使用相关子查询

SELECT nc.id, nc.name
  FROM night_club as nc
    INNER JOIN visitor_night_clubs as vnc ON nc.id = vnc.night_clubs_id 
    WHERE not exists 
         (select 1 from visitor_night_clubs as vnc1 where vnc.night_clubs_id=vnc1.night_clubs_id and vnc1.visitors_id=3)

Answer 2

禁止使用

SELECT nc.id, nc.name
  FROM night_club as nc
    INNER JOIN visitor_night_clubs as vnc ON nc.id = vnc.night_clubs_id 
    WHERE vnc.visitors_id not in( 3,....)

Answer 3

找出答案

SELECT *
    FROM night_club 
    WHERE night_club.id NOT IN 
(SELECT nc.id
  FROM night_club as nc
    INNER JOIN visitor_night_clubs as vnc ON nc.id = vnc.night_clubs_id 
    WHERE vnc.visitors_id = 4)

Answer 4

为此，我推荐not exists：

select nc.*
from night_club nc
where not exists (select 1
                  from visitor_night_clubs vnc
                  where vnc.night_clubs_id = nc.id and
                        vnc.visitors_id = 4
                 );

为什么NOT EXISTS比NOT IN好？原因很简单：当子查询返回的任何值为NOT IN时，NULL不会达到您的期望。这只会使使用变得危险。尽管您可以过滤掉NULL的值，但是始终使用NOT EXISTS意味着这永远不会成为问题。

还请注意使用表别名，并且子查询中不需要JOIN。

通过嵌套列表查找没有任何价值的所有实体

4 个答案: