一、查询语句（SELECT)
1、一般用法：
SELECT Column
FROM Table;
例1：
--从员工表里，选择姓名和工资
SELECT last_name, salary
FROM employees;
例2： --从员工表里,选择姓名和邮件,并将两列数据合成一列,以"员工邮件"为列名显示
SELECT last_name + ' 的电子邮件是: ' + last_name + [email=]'@testage.com'[/email] AS "员工电子邮件详细信息"
FROM employees;
2、过滤重复行：
SELECT DISTINCT Column
FROM Table;
例： --统计员工表里的工种分为几类
SELECT DISTINCT job_id
FROM employees;
3、增加选择条件：
SELECT Column
FROM Table
WHERE condition;
例1： --从员工表里，选择工资高于5000的员工
SELECT last_name, salary
FROM employees
WHERE salary > 5000;
例2： --从员工表里，选择工资高于5000，并且属于80号部门的员工
SELECT last_name, salary, department_id
FROM employees
WHERE salary > 5000 AND department_id = 80;
例3： --从员工表里，选择工资高于8000，或者属于80号部门的员工
SELECT last_name, department_id, salary 高于8000或者属于80号部门的员工
FROM employees
WHERE salary > 8000 OR department_id = 80;
例4： --从员工表里，选择年薪低于36000,并且没有奖金的员工信息
SELECT salary*12 年薪, *
FROM employees
WHERE salary*12 < 3000*12 AND commission_pct IS NULL;
例5: --从员工表里，选择工资在3000到5000之间（包含3000和5000）的员工信息
SELECT *
FROM employees
WHERE salary BETWEEN 3000 AND 5000;
例6： --从员工表里，选择属于20号部门，30号部门，80号部门的员工
SELECT last_name, department_id
FROM employees
WHERE department_id IN(20, 30, 80);--另一种写法：WHERE department_id = 20 OR department_id = 30 OR department_id = 80;
例7： --从员工表里，选择不属于20,30,80号部门的员工
SELECT last_name, department_id
FROM employees
WHERE department_id NOT IN(20, 30, 80);
4、模糊查询：
SELECT Column
FROM Table
WHERE keywords LIKE %_;
例1： --从员工表里，选择姓名以B打头的所有员工信息
SELECT *
FROM employees
WHERE last_name LIKE 'B%';
例2： --从员工表里，选择姓名第二个字母是a的所有员工信息
SELECT *
FROM employees
WHERE last_name LIKE '_a%';
例3： --从员工表里，选择姓名以A或B或C打头的员工信息
SELECT *
FROM employees
WHERE last_name LIKE '[A-C]%';
5、多表查询:
SELECT Table1.Column, Table2.Column
FROM Table1, Table2
WHERE Condition;
例1： --查询员工表里，所有员工所属的部门名字
SELECT employees.last_name, department.department_name
FROM employees, department
WHERE employees.department_id = department.department_id;
例2：--查询查询工资高于8000的员工所属的部门
SELECT e.last_name, e.salary, d.department_name
FROM employees e
INNER JOIN department d
ON e.salary > 8000 AND e.department_id = d.department_id;
例3： --查询所有员工所属的部门，即使该员工没有被分配任何部门
SELECT e.last_name, d.department_name
FROM employees e
LEFT OUTER JOIN department d
ON e.department_id = d.department_id;
例4： --查询每个部门所属的员工，即使该部门没有任何员工
SELECT d.department_name, e.last_name
FROM employees e
RIGHT OUTER JOIN department d
ON e.department_id = d.department_id;
例5：--查询所有部门以及所有员工，即使该部门没有任何员工或该员工没被分配任何部门
SELECT e.last_name, d.department_name
FROM employees e
FULL OUTER JOIN department d
ON e.department_id = d.department_id;
例6：--查询员工Baida的经理是谁
SELECT e.last_name 雇员, m.last_name 经理
FROM employees e, employees m
WHERE e.manager_id = m.employee_id
AND e.last_name = 'Baida';
二、组函数（AVG()、SUM()……）、分组函数（GROUP BY）、排序(ORDER BY)
1、组函数：
AVG(Column)
例： --统计全体员工的平均工资
SELECT AVG(salary) 平均工资
FROM employees;
SUM(Column)
例： --统计工资支出总额
SELECT SUM(salary) 工资支出总额
FROM employees;
MAX(Column)
例： --统计最高工资
SELECT MAX(salary) 最高工资
FROM employees;
MIN(Column)
例：--统计最低工资
SELECT MIN(salary) 最低工资
FROM employees;
COUNT(Column)
例：--统计员工总数
SELECT COUNT(employee_id) 员工总数
FROM employees;
2、分组函数：
GROUP BY Column
HAVING Condition
例：统计员工平均工资高于10000的部门
SELECT AVG(salary), department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary) > 10000;
3、排序：
ORDER BY
例1：将员工工资按升序排列
SELECT last_name, salary
FROM employees
ORDER BY salary;
例2：按员工入职时间长短降序排列
SELECT last_name, hire_date
FROM employees
ORDER BY hire_date DESC;
例3：查找工资最高的前三名员工
SELECT TOP 3 salary, last_name
FROM employees
ORDER BY salary DESC;
三、子查询
SELECT Column
FROM Table
WHERE express operator (SELECT Col
FROM Tab
WHERE condition)；
例1：--查找工资与Jones工资相同的员工信息
SELECT *
FROM employees
WHERE salary = (SELECT salary
FROM employees
WHERE last_name = 'Jones')；
例2：--查找员工表里，工资最高的员工的所有信息
SELECT *
FROM employees
WHERE salary = (SELECT MAX(salary)
FROM employees )；
例3：--查找最高工资高于10000，并且最低工资低于4000的部门
SELECT DISTINCT department_name
FROM department
WHERE department_id IN (SELECT department_id
FROM employees
GROUP BY department_id
HAVING MAX(salary) > 10000 AND MIN(salary) < 4000)；
例4： --选出表中后10行
SELECT *
FROM employees
WHERE employee_id NOT IN (SELECT TOP (((SELECT COUNT(employee_id)
FROM employees)) - 10) employee_id
FROM employees)；
四、增加(INSERT INTO Table VALUES=())、删除(DELETE FROM Table)、更改数据(UPDATE Table SET Column=key)
1、增加、插入数据：
INSERT INTO Table (Column1, Column2……)
VALUES (Element1, Element2……);
例1： --向部门表里插入编号为101的人事部
INSERT INTO department
VALUES (101, '人事部', NULL, NULL);
例2： --向员工表里插入编号为999，名字叫“测试时代”的新员工
INSERT INTO employees (employee_id, last_name)
VALUES (999, '测试时代');
2、删除数据：
DELETE FROM Table
WHERE Condition;
例： --删除部门表里标号为101的部门
DELETE FROM department
WHERE department_id = 101;
3、更新数据：
UPDATE Table
SET Column = Value
WHERE Condition;
例：--将部门号为80的部门，改为部门号为101，部门名为”人力资源部“
UPDATE department
SET department_id = 101,
department_name = '人力资源部'
WHERE department_id = 80;