Question

我有表部门和员工。架构就像，

department(id, name)
employee(id,depid,salary)

我需要得到每个部门的员工数量。我在mysql中的查询就像

select d.depname,count(e.id) 
from employe as e left join department as d on d.depid 
where e.depid=d.depid group by d.depid;

但结果集仅包含其中包含员工的部门。我需要那些拥有0名员工的部门为零。

Answer 1

只需交换表名，

SELECT  d.name, 
        COUNT(e.id) totalEmployeeCount
FROM    department AS d 
        LEFT JOIN employee AS e 
            ON e.depid = d.id
GROUP   BY d.id;

要进一步了解联接，请访问以下链接：

Visual Representation of SQL Joins

Answer 2

select d.depname,count(e.id) from employee as e 
right join department as d on d.depid = e.depid 
group by d.depid;

因此，请浏览http://dev.mysql.com/doc/refman/5.0/en/join.html

如何在Mysql Left Join中获取计数？

2 个答案: