Question

所以我有多个表，我正在尝试创建一个视图来显示我在select语句中返回的所有内容。但是，似乎mysql不允许创建具有子查询的视图。

所以不确定如何将其转换为视图。

Select  Title as "AlbumName" , 
        Sum(trk1.Price * trk1.Quant) as "TotalSales"
From    Album alb
        INNER JOIN
        (
            SELECT  AlbumId, 
                    t1.UnitPrice as "Price" , 
                    t1.Quantity as "Quant"
            FROM    Track trk
                    INNER JOIN
                    (
                        SELECT  TrackId, UnitPrice, Quantity
                        FROM    InvoiceLine
                        WHERE   InvoiceId IN ( SELECT InvoiceId FROM Invoice )
                    ) AS t1 ON (trk.TrackId = t1.TrackId)
        ) as trk1 ON (alb.AlbumId = trk1.AlbumId)
Group By alb.AlbumId

Answer 1

在VIEW中创建MySQL很简单，但有一些限制。 See HERE: MySQL View

其中一个限制是VIEW s不能包含在FROM子句中包含子查询的SELECT语句。因此，作为替代方案，首先为子查询创建一个包含IN子句的视图。

CREATE VIEW InvoiceLineView
AS
SELECT  DISTINCT a.*
FROM    InvoiceLine a
        INNER JOIN Invoice b
            ON a.InvoiceId = b.InvoiceId;

创建视图后，您现在可以继续加入原始查询中的视图，以便现在可以创建完全正常的VIEW。对于未计算的子查询，您不需要额外的视图。

CREATE VIEW AlbumSales
AS
Select  Title as AlbumName, 
        Sum(t1.UnitPrice * t1.Quantity) as TotalSales
From    Album alb
        INNER JOIN Track trk
            ON alb.AlbumId = trk1.AlbumId
        INNER JOIN InvoiceLineView t1
            ON trk.TrackId = t1.TrackId
Group   By alb.AlbumId;

虽然，MySQL中的VIEWS非常糟糕。

MySQL VIEW as performance troublemaker

Answer 2

如果你真的需要这个视图，你必须首先将子查询包装为视图。

CREATE VIEW vw_sub1 AS
SELECT TrackId, UnitPrice, Quantity
  FROM InvoiceLine
 WHERE InvoiceId
    IN (SELECT InvoiceId FROM Invoice);

CREATE VIEW vw_sub2 AS
SELECT AlbumId, t1.UnitPrice Price, t1.Quantity Quant
  FROM Track trk INNER JOIN 
       vw_sub1 t1 ON trk.TrackId = t1.TrackId;

CREATE VIEW vw_main AS
SELECT Title AlbumName, Sum(trk1.Price * trk1.Quant) TotalSales
  FROM Album alb INNER JOIN
       vw_sub2 trk1 ON alb.AlbumId = trk1.AlbumId
 GROUP BY alb.AlbumId;

代码未经过测试

Answer 3

不幸的是，MySQL在你的视图中不支持这样的子查询。我听说过的唯一解决方法是为每个子查询创建单独的视图，然后使用其他视图创建主视图。这有点奇怪，但确实如此。

在您的情况下，您需要创建3个视图 - 2个用于内部子查询，1个用于主要子视图。

从具有多个子查询/联接的Select语句创建视图

3 个答案: