Question

查询

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)

如何将上面的子查询更改为Correlated子查询？

Answer 1

我认为这是你正在寻找的东西。只需将查询移到FROM部分，然后使用JOIN根据WHERE子句中的相同条件过滤结果，除非您引用结果集（RS））子查询返回。

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

虽然这是有用的，但通过直接在SalesPerson表中使用JOIN可以更轻松，更快捷地完成。

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

你为什么这样做？对于简单的JOIN：

，这已经成熟

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

如果必须为此使用相关子查询，我能想到的唯一方法是：

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，子查询必须在外部查询的每次迭代中执行，这有时很有用，但同样，我在这里没有看到这一点。

Answer 3

检查评论以便更好地理解。

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

如何将subQuery更改为Correlated Subquery？

查询

3 个答案: