Question

我想弄清楚如何解决这个问题。

选择曾为IBM和Microsoft工作过的候选人。

与数据库关联的表包括

Candidate(Id,Name)
Company(Id,Name)
hasWorkedFor(CandidateId,CompanyId)

CandidateId和Company Id是Candidate表和Company表的外键。

我得到的查询是：

SELECT Candidate.Name 
FROM Candidate x, Candidate y, Company c1, Company c2, hasWorkedFor 
WHERE x.Id = Id 
  AND c1.Id = CompanyId
  AND c1.Name = "Microsoft" 
  AND c2.Id = CompanyId  
  AND c2.Name = "IBM";

任何帮助都将不胜感激。

Answer 1

试试这个：

select Candidate.* from Candidate inner join (
    select CandidateId from hasWorkedFor inner join Company
    on hasWorkedFor.CompanyId = Company.id
    where Company.name in ('IBM', 'Microsoft')
    group by CandidateId
    having count(distinct CompanyId) = 2
)t
on Candidate.Id = t.CandidateId

请注意，此查询还会为那些可能适用于其他公司的候选人提供。

如果您需要为IBM和Microsoft工作的候选人，那么您可以使用：

select Candidate.* from Candidate inner join (
    select t1.CandidateId from (
        select CandidateId   from hasWorkedFor inner join Company
        on hasWorkedFor.CompanyId = Company.id
        where Company.name in ('IBM', 'Microsoft')
        group by CandidateId
        having count(distinct CompanyId) = 2
    )t1 inner join(
        select CandidateId from hasWorkedFor 
        inner join Company
        on hasWorkedFor.CompanyId = Company.id
        group by CandidateId
        having count( distinct CompanyId ) = 2
    ) t2 on t1.CandidateId = t2.CandidateId
)t
on Candidate.Id = t.CandidateId

Answer 2

尝试此操作，如有任何疑问，请与我联系。

select a.name as candiate_name
from
   candidate a
left join
   hasworkedfor b
on a.id = b.candidateid
left join
   company c
on b.companyid = c.id
where c.name = 'Microsoft' and c.name  = 'IBM';

Answer 3

试试这段代码：

select candidate.name from candidate 
inner join hasworkedfor 
on candidate.id = hasworkedfor .candidateid inner join company 
on hasworkedfor .companyid = company.id 
where company.name = 'Microsoft' and company.name  = 'IBM'

Answer 4

SELECT ca.Name FROM Candidate ca 
    WHERE ca.Id IN (SELECT hw.CandidateId FROM hasWorkedFor hw 
                        LEFT OUTER JOIN Company co ON hw.CompanyId = co.Id WHERE co.Name = 'Microsoft') AND
          ca.Id IN (SELECT hw.CandidateId FROM hasWorkedFor hw 
                        LEFT OUTER JOIN Company co ON hw.CompanyId = co.Id WHERE co.Name = 'IBM')

或

SELECT ca.Name FROM Candidate ca 
    WHERE COUNT(SELECT DISTINCT hw.CompanyId FROM hasWorkedFor hw 
                        LEFT OUTER JOIN Company co ON hw.CompanyId = co.Id 
                        WHERE (co.Name = 'Microsoft' OR co.Name = 'IBM') AND hw.CandidateId = ca.Id) = 2

Answer 5

select * from Candidate c where
exists(select * from hasWorkedFor w where w.CandidateId=c.Id and w.CompanyId = 'Microsoft')
and exists(select * from hasWorkedFor w where w.CandidateId=c.Id and w.CompanyId = 'IBM')

换句话说，从Candidate中选择

他有一个在MSFT和
他有一个在IBM工作的条目

Answer 6

我的解决方案：

SELECT ca.Name
FROM Company cm
JOIN hasWorkedFor wk ON cm.Id = wk.CompanyId
JOIN Candidate ca ON wk.CandidateId = ca.Id
WHERE cm.Name IN ('IBM', 'Microsoft')
GROUP BY ca.Id,ca.Name
HAVING COUNT(*) = 2

SQL - 如何解决此查询？

6 个答案: