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

我实际上有两个问题。第一个是，上面的声明工作得很好。但是现在它将向他们的主管展示一堆员工。组织不好。顺便说一下，有三个主管。有没有办法让员工A和主管B与员工B一起说出主管A等等？

第二个问题是我还试图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没有工作。

Answer 1

一些事情

1）最好将连接谓词与连接保持一致。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）要由主管将它们保持在一起，只需使用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）要为每位主管计算员工数量，请使用group by和COUNT汇总功能

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

计算主管的员工人数

1 个答案: