Question

我有一张桌子最难

    One                        Two
   apple                      orange
   orange                     grapes 
   banana                     strawberry
   orange                     strawberry
   grapes                     apple

现在你可以看到我在这里列出了5对。让我告诉你，它不是一个普通的表，因为在这个表中，水果的名称（苹果）有时在第一列，有时在第二列。

And another table Description
name             color  
apple            red
orange           orange
strawberry       pink
banana           yellow
grapes           black

假设iam banana，我不想看到与我配对的水果的描述。 现在有人可以告诉我如何在mysql中显示与以下所有内容配对的水果的详细信息，但不包括香蕉：草莓，葡萄，苹果。

我告诉他们这样做的方法，这在mysql中是不受支持的。

Select * from description 
natural join (select one as name where two='apple' union select two as name where one='apple') as t1 
natural join (select one as name where two='grapes' union select two as name where one='grapes') as t2
natural join (select one as name where two='strawberry' union select two as name where one='strawberry') as t3
MINUS
Select * from description 
natural join (select one as name where two='banana' union select two as name where one='banana') as b6

Answer 1

SELECT * FROM Description
NATURAL JOIN (
  SELECT One AS name FROM hardest WHERE Two = 'strawberry'
  UNION
  SELECT Two AS name FROM hardest WHERE One = 'strawberry'
) AS t1
NATURAL JOIN (
  SELECT One AS name FROM hardest WHERE Two = 'grapes'
  UNION
  SELECT Two AS name FROM hardest WHERE One = 'grapes'
) AS t2
NATURAL JOIN (
  SELECT One AS name FROM hardest WHERE Two = 'apple'
  UNION
  SELECT Two AS name FROM hardest WHERE One = 'apple'
) AS t3;

<强>更新

OP更新了问题，添加了结果集应排除与banana配对的任何水果的约束;然后，他使用WHERE name NOT IN ( SELECT ... )提出了一个解决方案，但质疑外部联接是否会更有效。

首先，使用外部联接的查询：

SELECT Description.* FROM Description
NATURAL JOIN (
  SELECT One AS name FROM hardest WHERE Two = 'strawberry'
  UNION
  SELECT Two AS name FROM hardest WHERE One = 'strawberry'
) AS t1
NATURAL JOIN (
  SELECT One AS name FROM hardest WHERE Two = 'grapes'
  UNION
  SELECT Two AS name FROM hardest WHERE One = 'grapes'
) AS t2
NATURAL JOIN (
  SELECT One AS name FROM hardest WHERE Two = 'apple'
  UNION
  SELECT Two AS name FROM hardest WHERE One = 'apple'
) AS t3
NATURAL LEFT JOIN (
  SELECT One AS name, TRUE As hasBanana FROM hardest WHERE Two = 'banana'
  UNION
  SELECT Two AS name, TRUE As hasBanana FROM hardest WHERE One = 'banana'
) AS t4
WHERE hasBanana IS NULL;

关于哪个更有效，this article比较了不同的方法。它陈述（关于[NOT] IN ( SELECT ... )：

基本上，这与LEFT JOIN / IS NULL使用的计划完全相同，尽管这些计划由不同的代码分支执行，但它们在{{1}的结果中看起来不同}。实际上算法实际上是相同的，并且查询同时完成。

Answer 2

我正在清理我的答案，因为问题正在改变原来的问题。

Answer 3

您好你已经回答了自己的问题，你必须使用IN代替=。请检查以下查询...

select * from hardest,description where 
   (one=name and two IN ('apple' , 'strawberry','grapes')) 
   or 
   (one IN ('apple','strawberry' , 'grapes') and two=name)

感谢

Answer 4

请确保我写作的方式效率最高。如果您有其他方式更有效，请写下

 SELECT * FROM Description 
   NATURAL JOIN (   SELECT One AS name FROM hardest WHERE Two = 'strawberry'  
     UNION SELECT Two AS name FROM hardest WHERE One = 'strawberry' ) AS t1
   NATURAL JOIN (   SELECT One AS name FROM hardest WHERE Two = 'grapes'  
     UNION   SELECT Two AS name FROM hardest WHERE One = 'grapes' ) AS t2 
   NATURAL JOIN (   SELECT One AS name FROM hardest WHERE Two = 'apples' 
     UNION   SELECT Two AS name FROM hardest WHERE One = 'apples' ) AS t3
    where name not in ( SELECT One AS name FROM hardest WHERE Two = 'banana' 
     UNION   SELECT Two AS name FROM hardest WHERE One = 'banana') AS fz );

麻烦在mysql中选择查询

4 个答案: