題目描述

統計出當前各個title型別對應的員工當前薪水對應的平均工資。結果給出title以及平均工資avg。

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`));
CREATE TABLE IF NOT EXISTS "titles" (
`emp_no` int(11) NOT NULL,
`title` varchar(50) NOT NULL,
`from_date` date NOT NULL,
`to_date` date DEFAULT NULL);
 

解題思路

SELECT title , avg(salary) AS avg 
FROM titles t 
INNER JOIN salaries s
ON t.emp_no = s.emp_no 
AND t.to_date = '9999-01-01'
AND s.to_date = '9999-01-01'
group by t.title

• 平均工資需要用avg()函式
• 需要內連結２個表
• 根據題意需要group by 分組title
• 當前日期預設　‘9999-01-01’