如何在Mysql Left Join中計數？

Question

我有表部門和員工。 架構是什麼樣子，

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

我需要得到員工的數量在各個部門。 我在MySQL查詢像

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; 

但結果集只包含具有僱員的部門。 我需要有0名員工的部門本身爲零。

Answer 1

只是互換表名，

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; 

爲了進一步獲得更多的知識有關加入，請訪問以下鏈接：

• 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; 

至於原因，經過http://dev.mysql.com/doc/refman/5.0/en/join.html