Question

我试图了解如何有效地将谓词逻辑转换为SQL查询。我被困在：

For all P(x), (for all P(y), (Knows(x,y) -> Likes(x,y)))

我进一步翻译成：

-exists P(x), (exists P(y), (Knows(x,y) /\ -Likes(x,y)))

使用as＆＃39;公式＆＃39;：

for all x, (A -> B) <=> -exists x, (A /\ -B); for all x, (A) <=> -exists x, (-A)

如果出错的概率，这是最初的发音：

Write a query that returns the name of all persons that like everyone they know.

其中Knows和Likes表都不对称且只包含Person表的外键，因此表示Person X Knows / Likes Person Y。

对于以上内容，SQL SELECT查询的外观如何？

我试过这个但是没有工作：

SELECT P.name 
FROM Persons P 
WHERE NOT EXISTS (
    SELECT * 
    FROM Knows K 
    WHERE K.personB_id NOT IN (
        SELECT L.personB_id 
        FROM Likes L 
        WHERE K.personA_id = L.personA_id 
        AND K.personB_id <> L.personB_id))

Answer 1

查找了解他们不喜欢的人的列表。然后选择他们不在那里的人。

SELECT FROM Persons
    WHERE Persons.ID NOT IN (
        SELECT Knows.PersonA 
        FROM Knows LEFT JOIN Likes
        ON Knows.PersonA = Likes.PersonA
        AND Knows.PersonB = Likes.PersonB
        WHERE Likes.PersonB is null
   )

SQL：从谓词逻辑到SQL SELECT

1 个答案: