Question

我需要写一个查询来列出所有雇员的姓名（在1列中）和他们所监督的个人人数。

我已经尝试过将计数与concat结合使用，但是它不起作用，我只是不知道如何继续前进。

select 
  concat(Boss.firstName, ' ', Boss.lastName) as 'Boss', 
  concat(supervised.firstName, ' ',supervised.lastName) as supervised, 
  count(supervised.firstName, ' ',supervised.lastName)
from Employees as Boss
left join Employees as supervised on Boss.employeeNumber=supervised.reportsTo;

我需要第二列具有数值。我会为此提供任何帮助！

Answer 1

您需要在查询中添加分组并计算每个Boss的行数：

select 
  concat(Boss.firstName, ' ', Boss.lastName) as Boss, 
  count(supervised.lastName) counter
from Employees as Boss left join Employees as supervised 
on Boss.employeeNumber = supervised.reportsTo
group by concat(Boss.firstName, ' ', Boss.lastName)

Answer 2

您可以使用相关子查询。

SELECT concat(e1.firstname, ' ', e1.lastname) supervisor,
       (SELECT count(*)
               FROM employees e2
               WHERE e2.reportsto = e1.employeenumber) supervised_count
       FROM employees e1;

有没有一种方法可以计算concat语句？

2 个答案: