5

以下是我需要回答的提示：

列出每位员工的客户数量。包括员工的姓名和适当标记的客户数量，首先列出客户最多的员工。

以下是我的 EMPLOYEES 表：

create table EMPLOYEES
    (EmpID    char(4)         unique Not null,
     Ename    varchar(10),
     Job      varchar(9),
     MGR      char(4),
     Hiredate date,
     Salary   decimal(7,2),
     Comm     decimal(7,2),
     DeptNo   char(2)         not null,
         Primary key(EmpID),
         Foreign key(DeptNo) REFERENCES DEPARTMENTS(DeptNo));


insert into EMPLOYEES values (7839,'King','President',null,'17-Nov-11',5000,null,10);
insert into EMPLOYEES values (7698,'Blake','Manager',7839,'01-May-11',2850,null,30);
insert into EMPLOYEES values (7782,'Clark','Manager',7839,'02-Jun-11',2450,null,10);
insert into EMPLOYEES values (7566,'Jones','Manager',7839,'02-Apr-11',2975,null,20);
insert into EMPLOYEES values (7654,'Martin','Salesman',7698,'28-Feb-12',1250,1400,30);
insert into EMPLOYEES values (7499,'Allen','Salesman',7698,'20-Feb-11',1600,300,30);
insert into EMPLOYEES values (7844,'Turner','Salesman',7698,'08-Sep-11',1500,0,30);
insert into EMPLOYEES values (7900,'James','Clerk',7698,'22-Feb-12',950,null,30);
insert into EMPLOYEES values (7521,'Ward','Salesman',7698,'22-Feb-12',1250,500,30);
insert into EMPLOYEES values (7902,'Ford','Analyst',7566,'03-Dec-11',3000,null,20);
insert into EMPLOYEES values (7369,'Smith','Clerk',7902,'17-Dec-10',800,null,20);
insert into EMPLOYEES values (7788,'Scott','Analyst',7566,'09-Dec-12',3000,null,20);
insert into EMPLOYEES values (7876,'Adams','Clerk',7788,'12-Jan-10',1100,null,20);
insert into EMPLOYEES values (7934,'Miller','Clerk',7782,'23-Jan-12',1300,null,10);

以下是我的 CUSTOMERS 表：

create table CUSTOMERS
    (CustID      char(6)       unique Not null,
     Name        varchar(45),
     Address     varchar(40),
     City        varchar(30),
     State       varchar(2),
     Zip         varchar(9),
     AreaCode    char(3),
     Phone       varchar (9),
     RepID       char(4)       not null,
     CreditLimit decimal(9,2),
     Primary key(CustID),
         Foreign key(RepID) References EMPLOYEES(EmpID));


insert into CUSTOMERS values (100,'Jocksports','345 Viewridge','Belmont','CA','96711',415,'598-6609',7844,5000);
insert into CUSTOMERS values (101,'TKB Sport Shop','490 Boli Rd.','Redwood City','CA','94061',415,'368-1223',7521,10000);
insert into CUSTOMERS values (102,'Vollyrite','9722 Hamilton','Burlingame','CA','95133',415,'644-3341',7654,7000);
insert into CUSTOMERS values (103,'Just Tennis','Hillview Mall','Burlingame','CA','97544',415,'677-9312',7521,3000);
insert into CUSTOMERS values (104,'Every Mountain','574 Surry Rd.','Cupertino','CA','93301',408,'996-2323',7499,10000);
insert into CUSTOMERS values (105,'K + T Sports','3476 El Paseo','Santa Clara','CA','91003',408,'376-9966',7844,5000);
insert into CUSTOMERS values (106,'Shape Up','908 Sequoia','Palo Alto','CA','94301',415,'364-9777',7521,6000);
insert into CUSTOMERS values (107,'Womens Sports','Valco Village','Sunnyvale','CA','93301',408,'967-4398',7499,10000);
insert into CUSTOMERS values (108,'North Woods Fitness Supply Center','98 Lone Pine Way','Hibbing','MN','55649',612,'566-9123',7844,8000);

以下是我的查询：

select ename, empId
from EMPLOYEES
where EmpID in
(select count(repid) as NumberOfCustomers
from CUSTOMERS
group by RepID);

为什么我的查询不起作用？

我知道我想将 EMPLOYEES 中的 empid 与 CUSTOMERS 中的 repID 匹配，然后计算 rep ID 在 CUSTOMERS 中出现的次数。我需要 EMPLOYEES 表的唯一原因是输出 Ename。我对需要使用的语法感到困惑，因为我需要在 CUSTOMERS 表中输出 RepID 的计数

4

4 回答 4

1 
SELECT  *
FROM    employees e
CROSS APPLY
        (
        SELECT  COUNT(*)
        FROM    customers c
        WHERE   c.repId = e.empId
        ) cc (cnt)
ORDER BY
        cnt DESC

See this on SQLFiddle

The same with a subquery:

SELECT  *,
        (
        SELECT  COUNT(*)
        FROM    customers c
        WHERE   c.repId = e.empId
        ) cnt
FROM    employees e
ORDER BY
        cnt DESC
于 2013-04-17T21:36:55.683 回答
1

Common Table Expression如果您正在使用SQL Server 2005及以上，您也可以使用。

;WITH CTE
AS
(
   SELECT RepID, COUNT(*) AS CNT
   FROM CUSTOMERS 
   GROUP BY REPID  
)

SELECT E.Ename, E.EmpID, ISNULL(C.CNT, 0) 
FROM EMPLOYEES E
LEFT OUTER JOIN CTE C ON C.RepID = E.EmpID

演示

于 2013-04-17T21:47:00.953 回答
0

那这个呢？还是我误会了

 SELECT ename, count(*) as NumCustomers 
FROM Customers INNER JOIN 
 Employees ON customers.repid = employees.empid GROUP BY repid,ename 
 ORDER BY numCustomers DESC
于 2013-04-17T21:43:59.543 回答
0

您的内部查询只有一个count(repid)，这是一个计数，而不是您的外部查询需要的实际 EmployeeID where EmpID in (xxx)。不确定为什么要在内部查询中进行计数，因为您会在最终结果中丢失它，但这应该可以：

 select ename, empId
 from EMPLOYEES
 where EmpID in (
    select repID
    from CUSTOMERS);
于 2013-04-17T21:34:27.873 回答