【360天】我愛刷題系列119（2018.01.31）

叨叨兩句

1. ~

SQL習題014

1

題目描述
查找全部員工自入職以來的薪水漲幅狀況，給出員工編號emp_noy以及其對應的薪水漲幅growth，並按照growth進行升序
CREATE TABLE employees (
emp_no int(11) NOT NULL,
birth_date date NOT NULL,
first_name varchar(14) NOT NULL,
last_name varchar(16) NOT NULL,
gender char(1) NOT NULL,
hire_date date NOT NULL,
PRIMARY KEY (emp_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));

本題思路是先分別用兩次LEFT JOIN左鏈接employees與salaries，創建兩張表，分別存放員工當前工資（sCurrent）與員工入職時的工資（sStart），再用INNER JOIN鏈接sCurrent與sStart，最後限定在同一員工下用當前工資減去入職工資。

方法一：內層用LEFT JOIN，外層用INNER JOIN（內層也能夠改用 INNER JOIN）

SELECT sCurrent.emp_no, (sCurrent.salary-sStart.salary) AS growth
FROM (SELECT s.emp_no, s.salary FROM employees e LEFT JOIN salaries s ON e.emp_no = s.emp_no WHERE s.to_date = '9999-01-01') AS sCurrent
INNER JOIN (SELECT s.emp_no, s.salary FROM employees e LEFT JOIN salaries s ON e.emp_no = s.emp_no WHERE s.from_date = e.hire_date) AS sStart
ON sCurrent.emp_no = sStart.emp_no
ORDER BY growth

方法二：內外都層用FROM並列查詢

SELECT sCurrent.emp_no, (sCurrent.salary-sStart.salary) AS growth
FROM (SELECT s.emp_no, s.salary FROM employees e, salaries s WHERE e.emp_no = s.emp_no AND s.to_date = '9999-01-01') AS sCurrent,
(SELECT s.emp_no, s.salary FROM employees e, salaries s WHERE e.emp_no = s.emp_no AND s.from_date = e.hire_date) AS sStart
WHERE sCurrent.emp_no = sStart.emp_no
ORDER BY growth