统计主管的员工人数

Question

SELECT 
e.lname AS employee_name 
, s.lname AS supervisor_name 
, e.superssn AS supervisor_ssn 
FROM employee e INNER JOIN employee s 
WHERE e.superssn=s.ssn 

我其实有两个问题。第一个是，上面的声明工作得很好。但是现在，它会显示一群员工和他们的主管。组织不良。顺便说一下，有三名主管。有什么办法可以让我们说A和A，B和B，B和B？

第二个问题是，我也尝试只计算每个主管的员工数量，而不是用COUNT（）显示他们的名字，我尝试了几个不同的但不工作的员工。

Answer 1

有几件事情

1）这是很好的做法，让您的加入谓词您加入。所以改变：

FROM employee e INNER JOIN employee s WHERE e.superssn = s.ssn 

要：

FROM employee e INNER JOIN employee s ON e.superssn = s.ssn 

2）通过主管让他们在一起，只需使用一个order by：

SELECT 
    e.lname AS employee_name 
    , s.lname AS supervisor_name 
    , e.superssn AS supervisor_ssn 
FROM employee e INNER JOIN employee s ON e.superssn = s.ssn 
ORDER BY s.lname 

3）做员工的每一个的数主管使用group by和COUNT集合函数

SELECT 
    s.lname AS supervisor_name, 
    COUNT(*) AS employee_count 
FROM employee e INNER JOIN employee s ON e.superssn = s.ssn 
GROUP BY s.lname 
ORDER BY s.lname