mysql - 如何使用联接从两个表创建一个 View ，以显示另一个表的 COUNT？

Question

    CREATE VIEW EMPJOBS AS 
     SELECT EMPLOYEE.employee_id AS ENUM, 
     CONCAT(EMPLOYEE.first_name, 
     ' ' , EMPLOYEE.last_name) AS NAME, 
     EMPLOYEE.email AS EMAIL, 
     COUNT(JOBHISTORY.end_date) AS FINISHEDJOBS
    FROM EMPLOYEE, JOBHISTORY
    WHERE JOBHISTORY.employee_id = EMPLOYEE.employee_id;

这就是我的声明。我知道这是错误的，因为它显示的是:

它将 end_date 一起算作一个大计数。我怎样才能让它对每个单独的 ENUM 都有效？

谢谢!

Answer 1

在末尾添加group by子句。

CREATE VIEW EMPJOBS AS 
 SELECT 
     e.employee_id AS ENUM, 
     CONCAT(e.first_name, 
     ' ' , e.last_name) AS NAME, 
     e.email AS EMAIL, 
     COUNT(j.end_date) AS FINISHEDJOBS
FROM EMPLOYEE e 
inner join  JOBHISTORY j
on j.employee_id = e.employee_id
group by 
    e.employee_id
    ,CONCAT(e.first_name,' ', e.last_name)
    ,e.email;

作为最佳实践，尝试使用正确的连接语法来连接表，而不是使用逗号。还要为表名称添加别名以避免混淆和可读性。