Question

例如，如果我有球和盒子，球可以放在很多盒子里，盒子可以锁定，我怎样才能选择不在锁定盒子里的球？

balls
  id  name
  ==  ====
  1   in neither
  2   in unlocked
  3   in locked
  4   in both

boxes
  id  locked
  ==  ======
  1   0
  2   1

boxings
  ball_id box_id
  ======= ======
  2       1
  3       2
  4       1
  4       2

我已经使用左连接提出了这个问题，但它已经在＆＃34;中返回了＆＃34;球我想排除。

SELECT balls.* 
FROM balls 
LEFT OUTER JOIN boxings ON boxings.ball_id = balls.id 
LEFT OUTER JOIN boxes ON boxes.id = boxings.box_id 
WHERE (boxings.box_id IS NULL or boxes.locked = 0)
  AND boxes.id NOT IN (
    SELECT id FROM boxes WHERE locked = 1
    )

期望的结果：

id  name
==  ====
1   in neither
2   in unlocked

SQL小提琴： http://sqlfiddle.com/#!9/c26ab/4

Answer 1

我认为你的意思是：选择永远不会被锁在盒子里的球。

如果是这样，我会想到#burger-box > #cpBtn > div { transition-delay: 0.5s; } #burger-box > #cpBtn > div:first-child { transition-delay: 0s; } #burger-box > #cpBtn > div:last-child { transition-delay: 1s; }查询：

not exists

Answer 2

执行此操作的最简单方法可能是使用NOT EXISTS：

select id, name 
from balls 
where not exists (
  select NULL 
  from boxings 
  inner join boxes on boxes.id = boxings.box_id 
  where boxes.locked = 1
  and boxings.ball_id = balls.id
)

Answer 3

我觉得有趣的是，两个已经发布的答案都采用了同样略微奇怪的方法，将一些连接标准放在WHERE子句中：

inner join boxes on boxes.id = boxings.box_id
where boxes.locked = 1

最奇怪的是，我确信the same people advise elsewhere to not put join conditions in WHERE clauses。

无论如何，这是反连接方法的不同变体：

SELECT *
  FROM balls
 WHERE id NOT IN ( SELECT ball_id
                     FROM boxings
                          NATURAL JOIN 
                          ( SELECT id AS box_id FROM boxes WHERE locked = 1 )
                          NATURAL JOIN 
                          ( SELECT id AS ball_id FROM boxings ) );

排除列值的连接记录？

3 个答案: