这个SQL查询可以被简化吗？

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，我希望获得所有擅长某个特定体育项目的人员，而我只有体育“名称”属性可供我处理。要检索我已经想通了以下查询正确的行：

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')) 

现在的问题是，是不是有写这个查询更简单的方法？只用OR就行不通，因为我需要玩'网球'和'足球'的人。但使用AND也不起作用，因为这些值不在同一行。

Answer 1

你应该使用两个连接的查询：

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 2

您可以使用另一种JOIN避免了二次IN。子只选择返回那些玩的人都网球和足球：

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 3

诀窍是使用别名，这样就可以使用同一个表多次：

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 

或该：

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 

您需要申报UNIQUE KEY或 SportsPerPerson (sportsid, personid)以使其正确，快速地工作。

Answer 5

您需要查询的是：

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' 

也就是说，顺便说一句，在SportsPerPerson表中的ID密钥，是完全没有必要为了实现众多的你有很多的关系。使用PersonID和SportID列作为复合主键就足够了。