如何将subQuery更改为Co-related子查询？

Question

询问

SELECT FirstName,
    LastName
FROM AdventureWorks.Person.Contact a
INNER JOIN [AdventureWorks].[HumanResources].[Employee] b
    ON a.ContactID = b.ContactID
WHERE b.EmployeeID IN (
        SELECT SalesPersonID
        FROM AdventureWorks.Sales.SalesPerson c
        WHERE c.Bonus = 5000)

如何将上述子查询更改为与公司相关的子查询？

Answer 1

我认为这就是您要寻找的。 只需将查询移至FROM部分，并使用JOIN即可根据WHERE子句中的相同条件来过滤结果，只是这次您引用了子查询返回的结果集（RS）。

SELECT FirstName,
    LastName
FROM AdventureWorks.Person.Contact a
INNER JOIN [AdventureWorks].[HumanResources].[Employee] b
    ON a.ContactID = b.ContactID
INNER JOIN (SELECT SalesPersonID
        FROM AdventureWorks.Sales.SalesPerson c
        WHERE c.Bonus = 5000) AS RS ON b.EmpoyeeID = RS.SalesPersonID

尽管此功能有效，但可以通过直接对SalesPerson表使用JOIN来轻松，快速地完成操作。

SELECT FirstName,
    LastName
FROM AdventureWorks.Person.Contact a
INNER JOIN [AdventureWorks].[HumanResources].[Employee] b
    ON a.ContactID = b.ContactID
INNER JOIN SalesPersonID c 
    ON b.EmpoyeeID = c.SalesPersonID
    and c.bonus = 5000

Answer 2

为什么要这么做？ 一个简单的JOIN已经成熟了：

SELECT 
  FirstName,
  LastName
FROM AdventureWorks.Person.Contact a
INNER JOIN [AdventureWorks].[HumanResources].[Employee] b
  ON a.ContactID = b.ContactID
INNER JOIN AdventureWorks.Sales.SalesPerson c
  ON b.EmployeeID = c.SalesPersonID and c.Bonus = 5000

如果您必须为此使用相关子查询，那么我想到的唯一方法是：

SELECT 
  FirstName,
  LastName
FROM AdventureWorks.Person.Contact a
INNER JOIN [AdventureWorks].[HumanResources].[Employee] b
  ON a.ContactID = b.ContactID
WHERE 5000 IN (
    SELECT bonus
    FROM AdventureWorks.Sales.SalesPerson c
    WHERE c.SalesPersonID = b.employeeID)

在这种情况下，子查询将必须针对外部查询的每次迭代执行，这有时很有用，但是再次，我在这里看不到重点。

Answer 3

检查评论以更好地理解。

SELECT firstname,
       lastname
FROM   
    adventureworks.person.contact a
INNER JOIN 
    [AdventureWorks].[HumanResources].[employee] b ON a.contactid = b.contactid

INNER JOIN adventureworks.sales.salesperson c ON b.employeeid = c.salespersonid 

--if the below result not give satisfy answer, then comment below line and uncomment the comment line
AND c.bonus = 5000 --this will apply and might be give the dupliate entry.
--where c.bonus = 5000 --where cluase apply after all condiotion of inner join apply