Question

我有以下表格：
人，{“Id”，“姓名”，“姓氏”} 体育，{“Id”“姓名”，“类型”} SportsPerPerson，{“Id”，“PersonId”，“SportsId”}

对于我的查询，我希望得到所有超过特定运动项目的人员，而我只拥有运动“名称”属性。要检索正确的行，我已经找到了以下查询：

SELECT *
FROM Person
WHERE Person.Id in 
(
    SELECT SportsPerPerson.PersonId FROM SportsPerPerson
    INNER JOIN Sports on SportsPerPerson.SportsId = Sports.Id
    WHERE Sports.Name = 'Tennis'
)
AND Person.Id in 
(
    SELECT SportsPerPerson.PersonId FROM SportsPerPerson
    INNER JOIN Sports on SportsPerPerson.SportsId = Sports.Id
    WHERE Sports.Name = 'Soccer'
)

OR

SELECT *
FROM Person
WHERE Id IN
    (SELECT PersonId FROM SportsPerPerson WHERE SportsId IN 
        (SELECT Id FROM Sports WHERE Name = 'Tennis'))
AND Id IN
    (SELECT PersonId FROM SportsPerPerson WHERE SportsId IN 
        (SELECT Id FROM Sports WHERE Name = 'Soccer'))

现在我的问题是，是不是有更简单的方法来编写这个查询？使用OR不会起作用，因为我需要扮演'网球'和'足球'的人。但是使用AND也不起作用，因为值不在同一行上。

Answer 1

您可以使用其他JOIN来避免第二个IN。子选择只返回那些同时打网球和足球的人：

SELECT *
FROM Person
WHERE Person.Id IN
(
    SELECT spp1.PersonId
    FROM SportsPerPerson spp1
    JOIN SportsPerPerson spp2 ON ( spp2.PersonId = spp1.PersonId )
    JOIN Sports s1 on spp1.SportsId = s1.Id
    JOIN Sports s2 on spp2.SportsId = s2.Id
    WHERE s1.Name = 'Tennis'
      AND s2.Name = 'Soccer'
)

Answer 2

您应该在查询中使用两个联接：

SELECT *
FROM Person p INNER JOIN SportsPerPerson spp1 ON (p.PersonId = spp1.PersonId)
              INNER JOIN Sports s1 ON (s1.SportsIN = spp1.SportId)
              INNER JOIN SportsPerPerson spp2 ON (p.PersonId = spp2.PersonId)
              INNER JOIN Sports s2 ON (s2.SportId = spp2.SportId)
    WHERE s1.Name = 'Tennis' AND s2.Name='Soccer'

Answer 3

诀窍是使用别名，以便您可以多次使用相同的表：

SELECT p.*
FROM Person p
INNER JOIN SportsPerPerson spa
  ON p.Id = spa.PersonId
INNER JOIN Sports sa
  ON spa.SportsId = sa.Id
INNER JOIN SportsPerPerson spb
  ON p.Id = spb.PersonId
INNER JOIN Sports sb
  ON spb.SportsId = sb.Id
WHERE
  sa.Name = 'Tennis'
  AND sb.Name = 'Soccer'

Answer 4

此：

SELECT  *
FROM    Person p
WHERE   (
        SELECT  COUNT(*)
        FROM    Sports s
        JOIN    SportsPerPerson sp
        ON      sp.SportsID = s.id
        WHERE   s.name IN ('Tennis', 'Soccer')
                AND sp.PersonID = p.id
        ) = 2

或者这个：

SELECT  p.*
FROM    (
        SELECT  sp.PersonID
        FROM    Sports s
        JOIN    SportsPerPerson sp
        ON      sp.SportsID = s.id
        WHERE   s.name IN ('Tennis', 'Soccer')
        GROUP BY
                sp.PersonID
        HAVING  COUNT(*) = 2
        ) q
JOIN    person p
ON      p.id = q.personID

您需要在UNIQUE KEY上声明PRIMARY KEY或SportsPerPerson (sportsid, personid)才能正常，快速地工作。

Answer 5

您需要的查询是：

SELECT p.ID, p.Name, p.LastName
FROM Person p
JOIN SportsPerPerson sp ON p.ID = sp.PersonID 
JOIN Sports s ON sp.SportsID = s.ID
WHERE s.Name = 'Football'

这就是说，除此之外，SportsPerPerson表上的ID键完全没有必要实现你拥有的多对多关系。使用PersonID和SportID列作为复合主键就足够了。

这个SQL查询可以简化吗？

5 个答案: