题解
查找所有员工的last_name和first_name以及对应的dept_name
https://www.nowcoder.com/practice/5a7975fabe1146329cee4f670c27ad55
# SELECT e.last_name, e.first_name,
# CASE
# WHEN de.dept_no IS NULL THEN NULL
# ELSE d.dept_name
# END AS dept_name
# FROM employees e
# LEFT JOIN dept_emp de ON e.emp_no = de.emp_no
# LEFT JOIN departments d ON de.dept_no = d.dept_no;
SELECT last_name, first_name, dept_name
FROM employees AS e
LEFT JOIN (
SELECT emp_no, dept_name
FROM dept_emp AS de
LEFT JOIN departments AS d
ON de.dept_no = d.dept_no
) k
ON e.emp_no = k.emp_no;
