统计各个部门对应员工涨幅的次数总和,给出部门编码dept_no、部门名称dept_name以及次数sum
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`));
解决思路
SELECT d.dept_no,dp.dept_name,COUNT(s.salary) sum
FROM dept_emp d
INNER JOIN salaries s ON d.emp_no = s.emp_no
INNER JOIN departments dp ON d.dept_no = dp.dept_no
GROUP BY d.dept_no