mysql - 排除列值上的连接记录？

Question

例如，如果我有球和盒子，球可以在许多盒子中，并且盒子可以被锁定，我如何选择不在锁定盒子中的球？

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

我使用左连接想出了这个，但它返回“在两个”球 我想排除它。

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 fiddle : http://sqlfiddle.com/#!9/c26ab/4

Answer 1

我想你的意思是:选择永远不会在上锁的盒子里的球。

如果是这样，就会想到一个不存在查询:

select b.*
from balls b
where not exists (select 1
                  from boxings bxb join
                       boxes bo
                       on bxb.box_id = bo.id
                  where bxb.ball_id = b.id and bo.locked = 1
                 );