叨叨两句
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SQL习题007
1
找出所有员工当前(to_date='9999-01-01')具体的薪水salary情况，对于相同的薪水只显示一次,并按照逆序显示
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 distinct s.salary
from salaries s
where s.to_date = '9999-01-01'
order by s.salary desc;2
获取所有部门当前manager的当前薪水情况，给出dept_no, emp_no以及salary，当前表示to_date='9999-01-01'
CREATE TABLE dept_manager (dept_no char(4) NOT NULL,emp_no int(11) 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));
此题与前面第三题类似，思路如下：
1、先用INNER JOIN连接两张表，限制条件是两张表的emp_no相同，即d.emp_no = s.emp_no，并且将salaries用别名s代替，dept_manager用别名d代替
2、根据题意，要获取当前manager的当前salary情况，再加上限制条件d.to_date = '9999-01-01' AND s.to_date = '9999-01-01'即可（因为同一emp_no在salaries表中对应多条涨薪记录，而当s.to_date = '9999-01-01'时是该员工当前的薪水记录）
SELECT d.dept_no, d.emp_no, s.salary
FROM salaries AS s INNER JOIN dept_manager AS d
ON d.emp_no = s.emp_no
AND d.to_date = '9999-01-01'
AND s.to_date = '9999-01-01'select d.dept_no,d.emp_no,s.salary
from salaries s,dept_manager d
where d.emp_no = s.emp_no
and s.to_date = '9999-01-01'
and d.to_date = '9999-01-01';3
获取所有非manager的员工emp_no
CREATE TABLE dept_manager (dept_no char(4) NOT NULL,emp_no int(11) NOT NULL,from_date date NOT NULL,to_date date NOT NULL,
PRIMARY KEY (emp_no,dept_no));
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));
方法一：使用NOT IN选出在employees但不在dept_manager中的emp_no记录
SELECT emp_no FROM employees
WHERE emp_no NOT IN (SELECT emp_no FROM dept_manager)
方法二：先使用LEFT JOIN连接两张表，再从此表中选出dept_no值为NULL对应的emp_no记录
SELECT emp_no FROM (SELECT * FROM employees LEFT JOIN dept_manager
ON employees.emp_no = dept_manager.emp_no)
WHERE dept_no IS NULL
方法三：方法二的简版，使用单层SELECT语句即可
SELECT employees.emp_no FROM employees LEFT JOIN dept_manager
ON employees.emp_no = dept_manager.emp_no
WHERE dept_no IS NULL