题解 | #汇总各个部门当前员工的title类型的分配数目#

select de.dept_no,d.dept_name,t.title,count(t.title) as count
FROM departments as d
JOIN dept_emp as de ON d.dept_no = de.dept_no
JOIN titles as t ON de.emp_no = t.emp_no
WHERE de.to_date = '9999-01-01' and t.to_date = '9999-01-01'
GROUP BY de.dept_no,t.title
ORDER BY de.dept_no,t.title

• 重点在于group by