SQL練習22:各部門の給与記録数を統計する

CREATE TABLE `departments` (
`dept_no` char(4) NOT NULL,
`dept_name` varchar(40) NOT NULL,
PRIMARY KEY (`dept_no`));

CREATE TABLE `dept_emp` (
`emp_no` int(11) NOT NULL,
`dept_no` char(4) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`dept_no`));

CREATE TABLE `salaries` (
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`from_date`));

SELECT d.dept_no, dept_name, count(salary) sum
FROM dept_emp d JOIN departments dp
ON d.dept_no = dp.dept_no
JOIN salaries s
ON d.emp_no = s.emp_no
GROUP BY dept_no
ORDER BY dept_no