Question

我总是在PHP或ASAP中做到这一点，所以我觉得是时候实际学习在SQL中使用它的正确方法了。我在数据库中有以下4个表：

类别（字段：CategoryNumber，Desc）（包含15行的小表）

媒体（字段：MediaID，Desc，CategoryNumber等）（包含15,000行的大表）

销售（字段：日期，MediaID，EmployeeID等）（包含100,000行的大表）

员工（字段：EmployeeID，名称等）（只有20行的小表）

仅限类别链接到媒体媒体有类别和销售的链接。销售链接到媒体和员工员工只链接到销售

我想做的是写一个查询，告诉我某个员工从未销售任何媒体的类别。

我可以编写一个简单的查询来查找2个表之间的不匹配数据，但是当我处理4个表时，我不知道如何做到这一点。

感谢您的时间和帮助！

Answer 1

这是我的建议：

select *
from Category c
where not exists (
    select *
    from Employee e
    inner join Sales s on s.EmployeeId = e.EmployeeId
    inner join Media m on m.MediaID = s.MediaID
    where e.Name = 'Ryan' and m.CategoryNumber = c.CategoryNumber
)

要查询所有未出售任何类别的雇员：

select e.EmployeeName, c.CategoryNumber
from Category c
cross join Employee e
where not exists (
    select *
    from Sales s
    inner join Media m on m.MediaID = s.MediaID
    where c.categoryNumber = m.CategoryNumber
    and s.EmployeeId = e.EmployeeId
)

Answer 2

SELECT c.CategoryNumber, c.Desc
FROM   Category c
WHERE NOT EXISTS
(
SELECT *
FROM       Employees e
INNER JOIN Sales     s on s.EmployeeID = e.EmployeeID
INNER JOIN Media     m on m.MediaID    = s.MediaID
WHERE e.Name = "Ryan"
AND   m.CategoryNumber = c.CategoryNumber
)

MS Access显然需要很多括号（谢谢，Ryan！）：

select * 
from Category c 
where not exists 
( select * 
from (     Employee e 
inner join Sales    s on (s.EmployeeId = e.EmployeeId)) 
inner join Media    m on (m.MediaID    = s.MediaID) 
where (e.Name = 'Ryan' and m.CategoryNumber = c.CategoryNumber) )

Answer 3

select c.desc
from category
left outer join (select s.employeeid,m.categorynumber
         from sales s 
         inner join media m on s.mediaid=m.mediaid
         inner join employee e on e.employeeid=s.employeeid
         where e.name = 'JOE'
         group by employeeid,categorynumber) t on t.categorynumber=c.categorynumber
where s.employeeid is null

Answer 4

根据Carl在Access SQL语法中提供的解决方案修改了答案：


select *
from Category c
where not exists (
    select *
    from (Employee e
    inner join Sales s on (s.EmployeeId = e.EmployeeId))
    inner join Media m on (m.MediaID = s.MediaID)
    where (e.Name = 'Ryan' and m.CategoryNumber = c.CategoryNumber)
)

SQL：有4个表，希望找到无与伦比的数据

4 个答案: