sql查询，查找员工处理的订单

SQL查询，列出员工及其在数据库中处理的订单数量。输出列表必须包括员工ID、姓名和订单数量。列表必须按订单数量降序排列。我已在下面引用了所需的表格

CREATE TABLE employees
  (
    employee_id NUMBER 
                GENERATED BY DEFAULT AS IDENTITY START WITH 108 
                PRIMARY KEY,
    first_name VARCHAR( 255 ) NOT NULL,
    last_name  VARCHAR( 255 ) NOT NULL,
    email      VARCHAR( 255 ) NOT NULL,
    phone      VARCHAR( 50 ) NOT NULL ,
    hire_date  DATE NOT NULL          ,
    manager_id NUMBER( 12, 0 )        , -- fk
    job_title  VARCHAR( 255 ) NOT NULL,
    CONSTRAINT fk_employees_manager 
        FOREIGN KEY( manager_id )
        REFERENCES employees( employee_id )
        ON DELETE CASCADE
  );
-- product category
CREATE TABLE product_categories
  (
    category_id NUMBER 
                GENERATED BY DEFAULT AS IDENTITY START WITH 6 
                PRIMARY KEY,
    category_name VARCHAR2( 255 ) NOT NULL
  );

-- products table
CREATE TABLE products
  (
    product_id NUMBER 
               GENERATED BY DEFAULT AS IDENTITY START WITH 289 
               PRIMARY KEY,
    product_name  VARCHAR2( 255 ) NOT NULL,
    description   VARCHAR2( 2000 )        ,
    standard_cost NUMBER( 9, 2 )          ,
    list_price    NUMBER( 9, 2 )          ,
    category_id   NUMBER NOT NULL         ,
    CONSTRAINT fk_products_categories 
      FOREIGN KEY( category_id )
      REFERENCES product_categories( category_id ) 
      ON DELETE CASCADE
  );
-- customers
CREATE TABLE customers
  (
    customer_id NUMBER 
                GENERATED BY DEFAULT AS IDENTITY START WITH 320 
                PRIMARY KEY,
    name         VARCHAR2( 255 ) NOT NULL,
    address      VARCHAR2( 255 )         ,
    website      VARCHAR2( 255 )         ,
    credit_limit NUMBER( 8, 2 )
  );

CREATE TABLE orders
  (
    order_id NUMBER 
             GENERATED BY DEFAULT AS IDENTITY START WITH 106 
             PRIMARY KEY,
    customer_id NUMBER( 6, 0 ) NOT NULL, -- fk
    status      VARCHAR( 20 ) NOT NULL ,
    salesman_id NUMBER( 6, 0 )         , -- fk
    order_date  DATE NOT NULL          ,
    CONSTRAINT fk_orders_customers 
      FOREIGN KEY( customer_id )
      REFERENCES customers( customer_id )
      ON DELETE CASCADE,
    CONSTRAINT fk_orders_employees 
      FOREIGN KEY( salesman_id )
      REFERENCES employees( employee_id ) 
      ON DELETE SET NULL
  );
-- order items
CREATE TABLE order_items
  (
    order_id   NUMBER( 12, 0 )                                , -- fk
    item_id    NUMBER( 12, 0 )                                ,
    product_id NUMBER( 12, 0 ) NOT NULL                       , -- fk
    quantity   NUMBER( 8, 2 ) NOT NULL                        ,
    unit_price NUMBER( 8, 2 ) NOT NULL                        ,
    CONSTRAINT pk_order_items 
      PRIMARY KEY( order_id, item_id ),
    CONSTRAINT fk_order_items_products 
      FOREIGN KEY( product_id )
      REFERENCES products( product_id ) 
      ON DELETE CASCADE,
    CONSTRAINT fk_order_items_orders 
      FOREIGN KEY( order_id )
      REFERENCES orders( order_id ) 
      ON DELETE CASCADE
  );

我已经试过了

SELECT E.EMPLOYEE_ID,
       E.FIRSTNAME
       || ' '
       || E.LASTNAME,
       SUM(OI.QUANTITY * OI.UNITPRICE) AS TOTAL_SALES
  FROM ORDERS O
  JOIN EMPLOYEES E ON E.EMPLOYEE_ID = O.SALESMAN_ID
  JOIN ORDER_ITEMS OI ON O.ORDER_ID = OI.ORDER_ID
 GROUP BY E.EMPLOYEE_ID,
          E.FIRSTNAME,
          E.LASTNAME
 ORDER BY TOTAL_SALES DESC NULLS LAST;

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您可以按如下方式使用

分组依据

、

聚合

功能和

排序依据

：

SELECT E.EMPLOYEE_ID,
       E.FIRSTNAME
       || ' '
       || E.LASTNAME,
       SUM(OI.QUANTITY * OI.UNITPRICE) AS TOTAL_SALES
  FROM ORDERS O
  JOIN EMPLOYEES E ON E.EMPLOYEE_ID = O.SALESMAN_ID
  JOIN ORDER_ITEMS OI ON O.ORDER_ID = OI.ORDER_ID
 GROUP BY E.EMPLOYEE_ID,
          E.FIRSTNAME,
          E.LASTNAME
 ORDER BY 3 DESC NULLS LAST;

你能这样试试吗

SELECT EMPLOYEE_ID,
   EMPNAME,
   TOTAL_SALES
FROM (
SELECT E.EMPLOYEE_ID,
   E.FIRSTNAME
   || ' '
   || E.LASTNAME EMPNAME,
   SUM(OI.QUANTITY * OI.UNITPRICE) AS TOTAL_SALES
FROM ORDERS O
JOIN EMPLOYEES E ON E.EMPLOYEE_ID = O.SALESMAN_ID
JOIN ORDER_ITEMS OI ON O.ORDER_ID = OI.ORDER_ID
GROUP BY E.EMPLOYEE_ID,
      E.FIRSTNAME,
      E.LASTNAME)
ORDER BY TOTAL_SALES DESC NULLS LAST;   

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JOIN.JOIN.JOIN

第12行缺少一些表达式。我无法按最新答案中更新的顺序查找列号