Mysql 从表中识别匹配的记录

我有一个表

userSection

（问题表），它有一个

userSectionId

，我可以在任何答案表

isee\u answers\u 2013

或

isee\u answers\u 2014

或

isee\u answers\u 2015

或

isee\u answers\u 2016

中找到相应的答案。当前查询已被删除

select us.userSectionId,qs.questionSectionId,qs.questionId,us.userId,
case 
when a13.correct is not null then a13.answerId 
when a14.correct is not null then a14.answerId
when a15.correct is not null then a15.answerId
when a16.correct is not null then a16.answerId 
end 
as AnswerId,
case 
when a13.correct is not null then a13.correct 
when a14.correct is not null then a14.correct
when a15.correct is not null then a15.correct
when a16.correct is not null then a16.correct 
end 
as Correct,
case 
when a13.correct is not null then a13.duration 
when a14.correct is not null then a14.duration
when a15.correct is not null then a15.duration
when a16.correct is not null then a16.duration 
end 
as Duration
from userSections us
join questionSections qs on qs.sectionId = us.sectionId
JOIN
    userExams ue
ON
    ue.userExamId = us.userExamId
left join
isee_answers_2013.answers a13 on us.userSectionId=a13.userSectionId and us.UserId = a13.userId
left join
isee_answers_2014.answers a14 on us.userSectionId=a14.userSectionId and us.UserId = a14.userId
left join
isee_answers_2015.answers a15 on us.userSectionId=a15.userSectionId and us.UserId = a15.userId
left join
isee_answers_2016.answers a16 on us.userSectionId=a16.userSectionId and us.UserId = a16.userId
WHERE
    us.valid=1 and ue.userExamId=20467

---

是否有人可以验证并说这是正确的方法，或者是否有其他更好的方法可以做到这一点？

假设此逻辑正确，您可能只需要使用

coalesce（）

：

等等

---

逻辑并不完全相同。如果匹配答案上的

answerId

可以是

NULL

，那么这并不能满足您的需要。否则，这是表示此逻辑的一种更简单的方法。

假设此逻辑正确，您可能只需使用

coalesce（）

：

等等

逻辑并不完全相同。如果匹配答案上的

answerId

可以是

NULL

，那么这并不能满足您的需要。否则，这是一种更简单的表达这种逻辑的方法

coalesce(a13.answerId, a14.answerId, a15.answerId, a16.answerId) as answerId