mysql - 4个表的内连接

Question

表格

生产

类别

订单

订单详情

我已将 SalesView 制作如下

create view salesView as select o.oID, p.name as product, od.sell_price as price, od.qty as quantity, o.order_date
    from orderDetails od inner join
    orders o on o.oID = od.oID,
    production p where = p.ID = od.pID;

由于 od(表 OrderDetails 的实例)不包含对类别表的引用。如何在 SalesView 中添加“类别”列？

现在，

select * from SalesView;

我想在其中添加“类别”列。

我已经尝试过了...

create view salesView as select o.oID, p.name as product, c.name as category, od.sell_price as price, od.qty as quantity, o.order_date
    from orderDetails od inner join
    orders o on o.oID = od.oID,
    production p where = p.ID = od.pID,
    category c where c.ID = ???

Answer 1

不要混合符号/标准。要添加类别，只需将类别内部连接到您的生产表即可。这假设所有作品都有一个类别；否则您可能需要左(外)连接。

create view salesView as 
SELECT o.oID
     , p.name as product
     , c.name as category
     , od.sell_price as price
     , od.qty as quantity
     , o.order_date
     , c.name
FROM orderDetails od 
INNER JOIN orders o 
   on o.oID = od.oID
INNER JOIN Production p 
   on p.ID = od.pID
INNER JOIN Category c
   on c.ID = P.catID
WHERE...

不要这样做:

create view salesView as select o.oID, p.name as product, od.sell_price as price, od.qty as quantity, o.order_date
    from orderDetails od inner join --<See the inner join
    orders o on o.oID = od.oID, --<See the ,  (don't mix standards!)
    production p where = p.ID = od.pID;

注意标准的差异:https://gerardnico.com/data/type/relation/sql/join_default_ansi92_comparison