mysql - SQL 查询子查询结构

Question

我在使用 SQL 时遇到问题。我已经创建了一个餐厅的数据库，我正在尝试创建一个查询来显示为同一客户提供服务的主管和员工。

该Employee表有supervisor_id和employee_id。该Order表具有customer_id与employee_id该客户关联的 和 。我知道这涉及一个子查询，而且我知道它看起来像这样。

SELECT DISTINCT
        Employee.employee_id,
        Orders.customer_id,
        Employee.supervisor_id
FROM    Employee,
        Orders
WHERE   EXISTS ( SELECT customer_id,
                        Employee.employee_id
                 FROM   Orders AS cs2,
                        Employee
                 WHERE  cs2.employee_id = Employee.employee_id
                        AND Employee.supervisor_id = Employee.employee_id
                        AND cs2.customer_id = Orders.customer_id );

截至目前，此查询未返回任何结果。

Answer 1

可能是这样的：

SELECT a.employee_id, b.customer_id, a.supervisor_id
FROM   Employee a INNER JOIN Orders b ON a.employee_id = b.employee_id 
       INNER JOIN Orders c ON b.customer_id = c.customer_id
       AND c.employee_id = a.supervisor_id