SQL，计数不'；我的mysql查询不起作用

我正在使用mysql 5.1

这是我的数据库模式

office
+--------------+----------------+
| office_id    | office_name    |
+--------------+----------------+

employee
+--------------+-----------------------+------------+
| employee_id  | employee_hierarchy_id | office_id  |
+--------------+-----------------------+------------+

employee_hierarchy
+-----------------------+-------------------------------+
| employee_hierarchy_id | employee_hierarchy_description|
+-----------------------+-------------------------------+

我想对每个

办公室id

以下是我要求列出工厂id和员工id的请求：

SELECT office_id, employee_hierarchy_id
FROM office, employee_hierarchy
ORDER BY office_id ASC 

如果我尝试添加计数，它只显示一行：

SELECT office_id, employee_hierarchy_id, COUNT(*)
FROM office, employee_hierarchy
ORDER BY office_id ASC

---

添加

WHERE

consistion和

groupby

子句

SELECT office_id, employee_hierarchy_id, COUNT(*)
FROM office, employee_hierarchy
WHERE office.factory_id = employee_hierarchy.factory_id
GROUP BY office_id, employee_hierarchy_id
ORDER BY office_id ASC

或推荐的语法

更新1

如果您想在没有员工的情况下仍显示office记录，请使用

左联接

，否则使用

内部联接

SELECT  a.office_name , c.employee_hierarchy_description,
        COUNT(b.office_ID) totalCount
FROM    office a
        LEFT JOIN employee b
            ON a.office_ID = b.office_ID
        LEFT JOIN employee_hierarchy c
            ON b.employee_hierarchy_id = c.employee_hierarchy_id
GROUP BY a.office_name , c.employee_hierarchy_description
ORDER BY totalCount DESC

---

我找到了另一种方法，试试这个子查询

SELECT SUM(number_of_employees) as 'number of employee per factory',factory_id
FROM (
SELECT COUNT(*) as 'number_of_employees',employee.factory_id
FROM factory,employee
WHERE factory.factory_id = employee.factory_id
GROUP BY employee.employee_hierarchy_id
) AS tmptbl 
GROUP BY tmptbl.factory_id

---

希望这有帮助

您好，employee_hierarchy.factory_id不存在，我已通过添加我的employee_hierarchy表升级了我的db架构。“字段列表”中的未知列“b.employee_hierarchy_description”很抱歉应该是

c.employee_hierarchy_description

@Tom pouce否，正如您所见，表

employee

上有列

office_id

。是的，我的不好，这里发布的数据库模式与我的不完全相同。；）这工作做得很好。谢谢

SELECT SUM(number_of_employees) as 'number of employee per factory',factory_id
FROM (
SELECT COUNT(*) as 'number_of_employees',employee.factory_id
FROM factory,employee
WHERE factory.factory_id = employee.factory_id
GROUP BY employee.employee_hierarchy_id
) AS tmptbl 
GROUP BY tmptbl.factory_id