Question

以下sql查询有什么问题

select itemname from Item where itemid 
in

((select ItemID
 FROM Delivery NATURAL JOIN Supplier
 WHERE SupplierName = 'Nepalese Corp.')

 union

 (select ItemID
 FROM Sale NATURAL JOIN Department
 WHERE DepartmentName = 'Navigation'))

我在本网站上看过另一篇文章，建议删除两个联合集上的内括号，并为第一个联合集设置一个别名。我试过了，MYSQL在下面显示的行显示了一个x，但是，查询运行正常。我的问题是发生了什么？

select itemname from Item where itemid 
in

(select ItemID as id
 FROM Delivery NATURAL JOIN Supplier
 WHERE SupplierName = 'Nepalese Corp.'

 union

 select ItemID .          //shows an x at this line
 FROM Sale NATURAL JOIN Department
 WHERE DepartmentName = 'Navigation')

Answer 1

select itemname from Item 
where itemid in
(
    select ItemID 
    FROM Delivery 
    NATURAL JOIN Supplier WHERE SupplierName = 'Nepalese Corp.'
    union
    select ItemID
    FROM Sale 
    NATURAL JOIN Department WHERE DepartmentName = 'Navigation'
 )

您可以尝试以上代码。

只需删除不必要的括号即可解决问题。

Answer 2

您可以尝试将内部结果加入主表

 select itemname from Item as t1 join
    (select distinct ItemID
     FROM Delivery NATURAL JOIN Supplier
     WHERE SupplierName = 'Nepalese Corp.'
    union
    select distinct ItemID
     FROM Sale NATURAL JOIN Department
     WHERE DepartmentName = 'Navigation') as t2 on t1.ItemID=t2.ItemID

与union的MySQL错误

2 个答案: