Question

我正在创建一个虚拟数据仓库，并尝试加入2个单独的视图，每个视图都可以正常工作。但是，当合并时，group by语句中似乎有一些东西导致数据不正确。

create view CentreSizing as
select CentreID, Name,
case
  when Capacity between 0 and 199 then 'Small'
  when Capacity between 200 and 900 then 'Medium'
  else 'Large'
end as Size
from Centre;

create view sizeQuantities as
select cs.Size, count(*) as "Occurences" from
CentreSizing cs
group by cs.Size;

create view AvgSpendings2018 as
select cs.Size, monthname(d.DateStamp) as "Month", sum(e.Cost)/quant.Occurences as 
"AverageExpense"
from Expense e join CentreSizing cs on e.CentreID = cs.CentreID
join DateTime d on e.DateTimeID = d.DateTimeID
join sizeQuantities quant on quant.Size = cs.Size
where YEAR(d.DateStamp) = 2018
group by cs.Size, MONTH(d.DateStamp);

create view TotalSpendings2018 as
select e.CentreID, c.Name, cs.Size , monthname(d.DateStamp) as "Month", sum(e.Cost) as 
"TotalExpense" from Expense e
 left join DateTime d on e.DateTimeID = d.DateTimeID
 join Centre c on c.CentreID = e.CentreID
join CentreSizing cs on c.CentreID = cs.CentreID
where year(d.DateStamp) = 2018
group by month(d.DateStamp), e.CentreID;

所有视图创建都按预期的方式

select ts.CentreID, from TotalSpendings2018 ts join ts.Size = avg.Size Group by ts.CentreID, ts.Size,

| CentreID | Name | +----------+-------------------------- + |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        1 | Queen Alexandra Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        2 | Southampton General Hospital | |        3 | St Richard's Hospital | |        3 | St Richard's Hospital | |        3 | St Richard's Hospital |

Answer 1

视图TotalSpendings2018在GROUP BY子句中缺少c.Name（如果每个中心都有唯一的名称，那应该没问题）。尽管与大多数其他RDBMS不同，mysql允许这样做，但它易于出错，并且不是良好的编码习惯。

关于查询：

在我看来，实际上您不需要GROUP BY，因为没有使用聚合函数（否则，GROUP BY中缺少ts.Name和avg.AverageExpense）
从视图的描述中，我还会猜测您缺少“月份”的连接条件，因为该列在两个视图中均可用
为什么不在输出中显示TotalExpense？我会以为这就是您想要做的（否则，您不需要加入）

我对您的查询的期望值：

select 
    ts.CentreID,
    ts.Name, 
    ts.Size, 
    ts.Month, 
    avg.AverageExpense,
    ts.TotalExpense
from
    TotalSpendings2018 ts 
    join AvgSpendings2018 avg 
    on ts.Size = avg.Size
    and ts.Month = avg.Month

是否可以将两个具有重复数据的视图合并？

1 个答案: