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查找全部员工入职时候的薪水状况,给出emp_no以及salary, 并按照emp_no进行逆序
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
));测试
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
));spa
此题应注意如下四个知识点: 一、因为测试数据中,salaries.emp_no不惟一(由于号码为emp_no的员工会有屡次涨薪的可能,因此在salaries中对应的记录不止一条),employees.emp_no惟一,即salaries的数据会多于employees,所以需先找到employees.emp_no在salaries表中对应的记录salaries.emp_no,则有限制条件e.emp_no = s.emp_no 二、根据题意注意到salaries.from_date 和employees.hire_date的值应该要相等,所以有限制条件 e.hire_date = s.from_date 三、根据题意要按照emp_no值逆序排列,所以最后要加上 ORDER BY e.emp_no DESC 四、为了代码良好的可读性,运用了Alias别名语句,将employees简化为e,salaries简化为s,即 employees AS e与salaries AS s,其中AS能够省略 方法一:利用 INNER JOIN 链接两张表 SELECT e.emp_no, s.salary FROM employees AS e INNER JOIN salaries AS s ON e.emp_no = s.emp_no AND e.hire_date = s.from_date ORDER BY e.emp_no DESC 方法二:直接用逗号并列查询两张表 SELECT e.emp_no, s.salary FROM employees AS e, salaries AS s WHERE e.emp_no = s.emp_no AND e.hire_date = s.from_date ORDER BY e.emp_no DESC