subject ：

There is a department table departments A brief introduction is as follows :

There is one , Department employee relations form dept_emp A brief introduction is as follows :

There's a payroll salaries A brief introduction is as follows :

Please count the salary records of each department , Give the department code dept_no、 Department name dept_name And the Department salaries How many records are there in the table sum, according to dept_no Ascending sort , The output of the above example is as follows :

Answer key ：

After three tables are connected dept_no grouping , Calculation count 

select
    dp.dept_no,
    ds.dept_name,
    count(dp.dept_no)
from
    dept_emp dp
left join
    salaries s
on
    dp.emp_no = s.emp_no
join
    departments ds
on
    dp.dept_no = ds.dept_no
group by
    dp.dept_no 
order by
    dp.dept_no