MySQL 视图中不能有子查询，并且不维护顺序。如何从此查询创建视图？答案

【问题标题】：MySQL views cannot have subquery in from, and don't maintain order. How can I create a view from this query?MySQL 视图中不能有子查询，并且不维护顺序。如何从此查询创建视图？
【发布时间】：2011-06-28 21:32:23
【问题描述】：

我实际上是在尝试获取每个员工当前职位的结果集。我想从中创建一个视图以供以后使用，但我发现我被难住了，并且可能缺少一个简单的解决方案。这是有问题的查询，提前致谢！

select * from 
(SELECT
appointment.employee_id,
title.`name` as title_name
FROM
appointment
INNER JOIN appointment_title ON appointment.id = appointment_title.appointment_id
INNER JOIN title ON appointment_title.title_id = title.id
order by appointment_title.effective_date DESC) tmp group by employee_id

【问题讨论】：

标签： mysql view subquery

【解决方案1】：

更新：

SELECT
    appointment.employee_id ,
    ( SELECT title.`name`
      FROM appointment_title
        INNER JOIN title
          ON appointment_title.title_id = title.id
      WHERE appointment.id = appointment_title.appointment_id
      ORDER BY appointment_title.effective_date DESC
      LIMIT 1
    ) AS title_name
FROM appointment
GROUP BY appointment.employee_id

【讨论】：

【解决方案2】：

另一种选择是将查询分成两个视图。第一个视图将包含派生表子查询，第二个视图将简单地从中选择：

CREATE VIEW vwEmployee_Inner AS
SELECT
appointment.employee_id,
title.`name` as title_name
FROM
appointment
INNER JOIN appointment_title ON appointment.id = appointment_title.appointment_id
INNER JOIN title ON appointment_title.title_id = title.id
order by appointment_title.effective_date DESC

然后你原来的观点变成：

CREATE VIEW vwEmployee AS
SELECT * FROM vwEmployee_Inner GROUP BY employee_id

【讨论】：