内连接Sql查询答案

【问题标题】：Inner Join Sql Query内连接Sql查询
【发布时间】：2017-10-19 01:49:42
【问题描述】：

我有一个包含 3 个表格的问题：

1.Review(JobID)

2.Job(商号)

3.Business(BusinessNumber)（外键）。

我需要检索数据并创建具有 4 列 HighestBusiness、HighestRating、LowestBusiness、Lowest Rating 的表。

select business.businessname AS HIGHESTRATEDBUSINESS, 
        max(review.reviewrating) as HIGHEST
from business 
    inner join job 
        on job.selectedbusinessabnnumber=business.abnnumber 
    inner join review 
        on review.jobid=job.jobid 
where review.reviewrating = (select max(reviewrating)
                             from review)  
GROUP BY businessname 
UNION 
select business.businessname AS LOWESTRATEDBUSINESS, 
     MIN(review.reviewrating) as HIGHEST
from business 
    inner join job 
        on job.selectedbusinessabnnumber=business.abnnumber 
    inner join review 
         on review.jobid=job.jobid 
where review.reviewrating = (select MIN(reviewrating)
                               from review)
GROUP BY businessname
/

我现在还没有创建表格，我只是想显示四列。

【问题讨论】：

请提供一些样本和输出数据。您的查询是否返回任何行？？

标签： sql oracle join union

【解决方案1】：

UNION 运算符从具有相同投影的两个集合中生成一个结果集。您需要的是四列的新投影。所以将两个子查询变成内联视图并使用 CROSS JOIN：

select h.highestratedbusiness
       , h.highest
       , l.lowestratedbusiness
       , l.lowest
from
    (select business.businessname AS HIGHESTRATEDBUSINESS, 
            max(review.reviewrating) as HIGHEST
    from business 
        inner join job 
            on job.selectedbusinessabnnumber=business.abnnumber 
        inner join review 
            on review.jobid=job.jobid 
    where review.reviewrating = (select max(reviewrating)
                                from review)  
    GROUP BY businessname ) h
cross join 
        (select business.businessname AS LOWESTRATEDBUSINESS, 
             MIN(review.reviewrating) as HIGHEST
        from business 
            inner join job 
                on job.selectedbusinessabnnumber=business.abnnumber 
            inner join review 
                 on review.jobid=job.jobid 
        where review.reviewrating = (select MIN(reviewrating)
                                       from review)
        GROUP BY businessname ) l
/

CROSS JOIN 为连接集中的每个记录组合生成一条记录。当数据产生一项最高评级的业务和一项最低评级的业务时，这将很好。但如果其中一个或两个地方存在平局，它将生成笛卡尔积。有很多方法可以解决这个问题，所以如果这对您来说是一个障碍，请完善您的问题。

【讨论】：