6天掌握MySQL基础--day3

SQL92语法连接查询测试和复习

SQL92语法连接查询测试

#1.显示所有员工的姓名，部门号和部门名称。
USE myemployees ;

SELECT 
    last_name,
    d.department_id,
    department_name 
FROM
    employees e,
    departments d 
WHERE e.`department_id` = d.`department_id` ;

#2.查询90号部门员工的job_id和90号部门的location_id
SELECT 
    job_id,
    location_id 
FROM
    employees e,
    departments d 
WHERE e.`department_id` = d.`department_id` 
    AND e.`department_id` = 90 ;

#3.	选择所有有奖金的员工的
last_name,
department_name,
location_id,
city 
SELECT 
    last_name,
    department_name,
    l.location_id,
    city 
FROM
    employees e,
    departments d,
    locations l 
WHERE e.department_id = d.department_id 
    AND d.location_id = l.location_id 
    AND e.commission_pct IS NOT NULL ;

#4.选择city在Toronto工作的员工的
last_name,
job_id,
department_id,
department_name 
SELECT 
    last_name,
    job_id,
    d.department_id,
    department_name 
FROM
    employees e,
    departments d,
    locations l 
WHERE e.department_id = d.department_id 
    AND d.location_id = l.location_id 
    AND city = 'Toronto' ;

#5.查询每个工种、每个部门的部门名、工种名和最低工资
SELECT 
    department_name,
    job_title,
    MIN(salary) 最低工资 
FROM
    employees e,
    departments d,
    jobs j 
WHERE e.`department_id` = d.`department_id` 
    AND e.`job_id` = j.`job_id` 
GROUP BY department_name,
    job_title ;

#6.查询每个国家下的部门个数大于2的国家编号
SELECT 
    country_id,
    COUNT(*) 部门个数 
FROM
    departments d,
    locations l 
WHERE d.`location_id` = l.`location_id` 
GROUP BY country_id 
HAVING 部门个数 > 2 ;

#7、选择指定员工的姓名，员工号，以及他的管理者的姓名和员工号，结果类似于下面的格式
employees Emp #	manager	Mgr#
kochhar 101 king 100 
SELECT 
    e.last_name employees,
    e.employee_id "Emp#",
    m.last_name manager,
    m.employee_id "Mgr#" 
FROM
    employees e,
    employees m 
WHERE e.manager_id = m.employee_id 
    AND e.last_name = 'kochhar' ;

复习
day2的学习内容

DQL语言学习

进阶6：连接查询（接day2）

连接查询详解

#二、sql99语法
/*
语法：
	select 查询列表
	from 表1 别名 【连接类型】
	join 表2 别名 
	on 连接条件
	【where 筛选条件】
	【group by 分组】
	【having 筛选条件】
	【order by 排序列表】
	

分类：
内连接(★)：inner
外连接
	左外(★):left 【outer】
	右外(★)：right 【outer】
	全外：full【outer】
交叉连接：cross 

*/
#一）内连接
/*
语法：

select 查询列表
from 表1 别名
inner join 表2 别名
on 连接条件;

分类：
等值
非等值
自连接

特点：
①添加排序、分组、筛选
②inner可以省略
③筛选条件放在where后面，连接条件放在on后面，提高分离性，便于阅读
④inner join连接和sql92语法中的等值连接效果是一样的，都是查询多表的交集
*/
#1、等值连接
#案例1.查询员工名、部门名
SELECT 
    last_name,
    department_name 
FROM
    departments d 
    JOIN employees e 
        ON e.`department_id` = d.`department_id` ;

#案例2.查询名字中包含e的员工名和工种名（添加筛选）
SELECT 
    last_name,
    job_title 
FROM
    employees e 
    INNER JOIN jobs j 
        ON e.`job_id` = j.`job_id` 
WHERE e.`last_name` LIKE '%e%' ;

#3. 查询部门个数>3的城市名和部门个数，（添加分组+筛选）
#①查询每个城市的部门个数
#②在①结果上筛选满足条件的
SELECT 
    city,
    COUNT(*) 部门个数 
FROM
    departments d 
    INNER JOIN locations l 
        ON d.`location_id` = l.`location_id` 
GROUP BY city 
HAVING COUNT(*) > 3 ;

#案例4.查询哪个部门的员工个数>3的部门名和员工个数，并按个数降序（添加排序）
#①查询每个部门的员工个数
SELECT 
    COUNT(*),
    department_name 
FROM
    employees e 
    INNER JOIN departments d 
        ON e.`department_id` = d.`department_id` 
GROUP BY department_name 

#② 在①结果上筛选员工个数>3的记录，并排序
SELECT 
    COUNT(*) 个数,
    department_name 
FROM
    employees e 
    INNER JOIN departments d 
        ON e.`department_id` = d.`department_id` 
GROUP BY department_name 
HAVING COUNT(*) > 3 
ORDER BY COUNT(*) DESC ;

#5.查询员工名、部门名、工种名，并按部门名降序（添加三表连接）
SELECT 
    last_name,
    department_name,
    job_title 
FROM
    employees e 
    INNER JOIN departments d 
        ON e.`department_id` = d.`department_id` 
    INNER JOIN jobs j 
        ON e.`job_id` = j.`job_id` 
ORDER BY department_name DESC ;

#二）非等值连接
#查询员工的工资级别
SELECT 
    salary,
    grade_level 
FROM
    employees e 
    JOIN job_grades g 
        ON e.`salary` BETWEEN g.`lowest_sal` 
        AND g.`highest_sal` ;

#查询工资级别的个数>20的个数，并且按工资级别降序
SELECT 
    COUNT(*),
    grade_level 
FROM
    employees e 
    JOIN job_grades g 
        ON e.`salary` BETWEEN g.`lowest_sal` 
        AND g.`highest_sal` 
GROUP BY grade_level 
HAVING COUNT(*) > 20 
ORDER BY grade_level DESC ;

#三）自连接
#查询员工的名字、上级的名字
SELECT 
    e.last_name,
    m.last_name 
FROM
    employees e 
    JOIN employees m 
        ON e.`manager_id` = m.`employee_id` ;

#查询姓名中包含字符k的员工的名字、上级的名字
SELECT 
    e.last_name,
    m.last_name 
FROM
    employees e 
    JOIN employees m 
        ON e.`manager_id` = m.`employee_id` 
WHERE e.`last_name` LIKE '%k%' ;

#二、外连接
/*
 应用场景：用于查询一个表中有，另一个表没有的记录
 
 特点：
 1、外连接的查询结果为主表中的所有记录
	如果从表中有和它匹配的，则显示匹配的值
	如果从表中没有和它匹配的，则显示null
	外连接查询结果=内连接结果+主表中有而从表没有的记录
 2、左外连接，left join左边的是主表
    右外连接，right join右边的是主表
 3、左外和右外交换两个表的顺序，可以实现同样的效果 
 4、全外连接=内连接的结果+表1中有但表2没有的+表2中有但表1没有的
 */
#引入：查询男朋友不在男神表的的女神名
SELECT 
    * 
FROM
    beauty ;

SELECT 
    * 
FROM
    boys ;

#左外连接
SELECT 
    b.*,
    bo.* 
FROM
    boys bo 
    LEFT OUTER JOIN beauty b 
        ON b.`boyfriend_id` = bo.`id` 
WHERE b.`id` IS NULL ;

#案例1：查询哪个部门没有员工
#左外
SELECT 
    d.*,
    e.employee_id 
FROM
    departments d 
    LEFT OUTER JOIN employees e 
        ON d.`department_id` = e.`department_id` 
WHERE e.`employee_id` IS NULL ;

#右外
SELECT 
    d.*,
    e.employee_id 
FROM
    employees e 
    RIGHT 
    OUTER JOIN departments d 
        ON d.`department_id` = e.`department_id` 
WHERE e.`employee_id` IS NULL ;

#全外,mysql不支持
USE girls ;

SELECT 
    b.*,
    bo.* 
FROM
    beauty b FULL 
    OUTER JOIN boys bo 
        ON b.`boyfriend_id` = bo.id ;

#三）交叉连接（笛卡尔乘积）
SELECT 
    b.*,
    bo.* 
FROM
    beauty b 
    CROSS JOIN boys bo ;

#sql92和sql99 pk
/*
 功能：sql99支持的较多
 可读性：sql99实现连接条件和筛选条件的分离，可读性较高
 */

连接查询测试

#一、查询编号>3的女神的男朋友信息，如果有则列出详细，如果没有，用null填充
SELECT 
    b.id,
    b.name,
    bo.* 
FROM
    beauty b 
    LEFT OUTER JOIN boys bo 
        ON b.`boyfriend_id` = bo.`id` 
WHERE b.`id` > 3 ;

#二、查询哪个城市没有部门
SELECT 
    city 
FROM
    departments d 
    RIGHT 
    OUTER JOIN locations l 
        ON d.`location_id` = l.`location_id` 
WHERE d.`department_id` IS NULL ;

#三、查询部门名为SAL或IT的员工信息
SELECT 
    e.*,
    d.department_name,
    d.`department_id` 
FROM
    departments d 
    LEFT JOIN employees e 
        ON d.`department_id` = e.`department_id` 
WHERE d.`department_name` IN ('SAL', 'IT') ;

进阶7：子查询

/*
含义：
出现在其他语句中的select语句，称为子查询或内查询
外部的查询语句，称为主查询或外查询

分类：
按子查询出现的位置：
	select后面：
		仅仅支持标量子查询
		
	from后面：
		支持表子查询
		
	where或having后面：★
		标量子查询（单行） √
		列子查询  （多行） √
		
		行子查询
		
	exists后面（相关子查询）
		表子查询
		
按结果集的行列数不同：
	标量子查询（结果集只有一行一列）
	列子查询（结果集只有一列多行）
	行子查询（结果集有一行多列）
	表子查询（结果集一般为多行多列）
*/
#一、where或having后面
/*
1、标量子查询（单行子查询）
2、列子查询（多行子查询）

3、行子查询（多列多行）

特点：
①子查询放在小括号内
②子查询一般放在条件的右侧
③标量子查询，一般搭配着单行操作符使用
> < >= <= = <>

列子查询，一般搭配着多行操作符使用
in、any/some、all

④子查询的执行优先于主查询执行，主查询的条件用到了子查询的结果

*/

子查询详解

#1.标量子查询★
#案例1：谁的工资比 Abel 高?
#①查询Abel的工资
SELECT 
    salary 
FROM
    employees 
WHERE last_name = 'Abel' 

#②查询员工的信息，满足 salary>①结果
SELECT 
    * 
FROM
    employees 
WHERE salary > 
    (SELECT 
        salary 
    FROM
        employees 
    WHERE last_name = 'Abel') ;

#案例2：返回job_id与141号员工相同，salary比143号员工多的员工 姓名，job_id 和工资
#①查询141号员工的job_id
SELECT 
    job_id 
FROM
    employees 
WHERE employee_id = 141 

#②查询143号员工的salary
SELECT 
    salary 
FROM
    employees 
WHERE employee_id = 143 
    
#③查询员工的姓名，job_id 和工资，要求job_id=①并且salary>②
SELECT 
    last_name,
    job_id,
    salary 
FROM
    employees 
WHERE job_id = 
    (SELECT 
        job_id 
    FROM
        employees 
    WHERE employee_id = 141) 
    AND salary > 
    (SELECT 
        salary 
    FROM
        employees 
    WHERE employee_id = 143) ;

#案例3：返回公司工资最少的员工的last_name,job_id和salary
#①查询公司的 最低工资
SELECT 
    MIN(salary) 
FROM
    employees 
    
#②查询last_name,job_id和salary，要求salary=①
SELECT 
    last_name,
    job_id,
    salary 
FROM
    employees 
WHERE salary = 
    (SELECT 
        MIN(salary) 
    FROM
        employees) ;

#案例4：查询最低工资大于50号部门最低工资的部门id和其最低工资
#①查询50号部门的最低工资
SELECT 
    MIN(salary) 
FROM
    employees 
WHERE department_id = 50 ;

#②查询每个部门的最低工资
SELECT 
    MIN(salary),
    department_id 
FROM
    employees 
GROUP BY department_id ;
    
#③在②基础上筛选，满足min(salary)>①
SELECT 
    MIN(salary),
    department_id 
FROM
    employees 
GROUP BY department_id 
HAVING MIN(salary) > 
    (SELECT 
        MIN(salary) 
    FROM
        employees 
    WHERE department_id = 50) ;

#非法使用标量子查询
SELECT 
    MIN(salary),
    department_id 
FROM
    employees 
GROUP BY department_id 
HAVING MIN(salary) > 
    (SELECT 
        salary 
    FROM
        employees 
    WHERE department_id = 250) ;

#2.列子查询（多行子查询）★
#案例1：返回location_id是1400或1700的部门中的所有员工姓名
#①查询location_id是1400或1700的部门编号
SELECT DISTINCT    # 去重提高效率
    department_id 
FROM
    departments 
WHERE location_id IN (1400, 1700) ;

#②查询员工姓名，要求部门号是①列表中的某一个
SELECT 
    last_name 
FROM
    employees 
WHERE department_id IN 
    (SELECT DISTINCT 
        department_id 
    FROM
        departments 
    WHERE location_id IN (1400, 1700)) ;

#案例2：返回其它工种中比job_id为‘IT_PROG’工种任一工资低的员工的员工号、姓名、job_id 以及salary
#①查询job_id为‘IT_PROG’部门任一工资
SELECT DISTINCT 
    salary 
FROM
    employees 
WHERE job_id = 'IT_PROG' ;

#②查询员工号、姓名、job_id 以及salary，salary<(①)的任意一个
SELECT 
    last_name,
    employee_id,
    job_id,
    salary 
FROM
    employees 
WHERE salary < ANY 
    (SELECT DISTINCT 
        salary 
    FROM
        employees 
    WHERE job_id = 'IT_PROG') 
    AND job_id <> 'IT_PROG' ;

#或
SELECT 
    last_name,
    employee_id,
    job_id,
    salary 
FROM
    employees 
WHERE salary < 
    (SELECT 
        MAX(salary) 
    FROM
        employees 
    WHERE job_id = 'IT_PROG') 
    AND job_id <> 'IT_PROG' ;

#案例3：返回其它工种中比job_id为‘IT_PROG’工种所有工资都低的员工的员工号、姓名、job_id 以及salary
SELECT 
    last_name,
    employee_id,
    job_id,
    salary 
FROM
    employees 
WHERE salary < ALL 
    (SELECT DISTINCT 
        salary 
    FROM
        employees 
    WHERE job_id = 'IT_PROG') 
    AND job_id <> 'IT_PROG' ;

#或
SELECT 
    last_name,
    employee_id,
    job_id,
    salary 
FROM
    employees 
WHERE salary < 
    (SELECT 
        MIN(salary) 
    FROM
        employees 
    WHERE job_id = 'IT_PROG') 
    AND job_id <> 'IT_PROG' ;

#3、行子查询（结果集一行多列或多行多列）
#案例：查询员工编号最小并且工资最高的员工信息
SELECT 
    * 
FROM
    employees 
WHERE (employee_id, salary) =   # 局限性
    (SELECT 
        MIN(employee_id),
        MAX(salary) 
    FROM
        employees) ;

#①查询最小的员工编号
SELECT 
    MIN(employee_id) 
FROM
    employees ;
    
#②查询最高工资
SELECT 
    MAX(salary) 
FROM
    employees ;

       
#③查询员工信息
SELECT 
    * 
FROM
    employees 
WHERE employee_id = 
    (SELECT 
        MIN(employee_id) 
    FROM
        employees) 
    AND salary = 
    (SELECT 
        MAX(salary) 
    FROM
        employees) ;

#二、select后面
/*
仅仅支持标量子查询
*/
#案例：查询每个部门的员工个数
SELECT 
    d.*,
    (SELECT 
        COUNT(*) 
    FROM
        employees e 
    WHERE e.department_id = d.`department_id`) 个数 
FROM
    departments d ;

#案例2：查询员工号=102的部门名
SELECT 
    (SELECT 
        department_name
    FROM
        departments d 
        INNER JOIN employees e 
            ON d.department_id = e.department_id 
    WHERE e.employee_id = 102) 部门名 ;

#三、from后面
/*
将子查询结果充当一张表，要求必须起别名
*/
#案例：查询每个部门的平均工资的工资等级
#①查询每个部门的平均工资
SELECT 
    AVG(salary),
    department_id 
FROM
    employees 
GROUP BY department_id 
    SELECT 
        * 
    FROM
        job_grades ;

#②连接①的结果集和job_grades表，筛选条件平均工资 between lowest_sal and highest_sal
SELECT 
    ag_dep.*,
    g.`grade_level` 
FROM
    (SELECT 
        AVG(salary) ag,
        department_id 
    FROM
        employees 
    GROUP BY department_id) ag_dep 
    INNER JOIN job_grades g 
        ON ag_dep.ag BETWEEN lowest_sal 
        AND highest_sal ;

#四、exists后面（相关子查询）
/*
语法：
exists(完整的查询语句)
结果：
1或0
*/
SELECT 
    EXISTS 
    (SELECT 
        employee_id 
    FROM
        employees 
    WHERE salary = 300000) ;

#案例1：查询有员工的部门名
#in
SELECT 
    department_name 
FROM
    departments d 
WHERE d.`department_id` IN 
    (SELECT 
        department_id 
    FROM
        employees) ;
        
#exists
SELECT 
    department_name 
FROM
    departments d 
WHERE EXISTS 
    (SELECT 
        * 
    FROM
        employees e 
    WHERE d.`department_id` = e.`department_id`) ;


#案例2：查询没有女朋友的男神信息
#in
SELECT 
    bo.* 
FROM
    boys bo 
WHERE bo.id NOT IN 
    (SELECT 
        boyfriend_id 
    FROM
        beauty) ;
        
#exists
SELECT 
    bo.* 
FROM
    boys bo 
WHERE NOT EXISTS 
    (SELECT 
        boyfriend_id 
    FROM
        beauty b 
    WHERE bo.`id` = b.`boyfriend_id`) ;

子查询测试

#1.	查询和Zlotkey相同部门的员工姓名和工资
#①查询Zlotkey的部门
SELECT 
    department_id 
FROM
    employees 
WHERE last_name = 'Zlotkey' ;

#②查询部门号=①的姓名和工资
SELECT 
    last_name,
    salary 
FROM
    employees 
WHERE department_id = 
    (SELECT 
        department_id 
    FROM
        employees 
    WHERE last_name = 'Zlotkey') ;

#2.查询工资比公司平均工资高的员工的员工号，姓名和工资。
#①查询平均工资
SELECT 
    AVG(salary) 
FROM
    employees ;

#②查询工资>①的员工号，姓名和工资。
SELECT 
    last_name,
    employee_id,
    salary 
FROM
    employees 
WHERE salary > 
    (SELECT 
        AVG(salary) 
    FROM
        employees) ;

#3.查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资
#①查询各部门的平均工资
SELECT 
    AVG(salary),
    department_id 
FROM
    employees 
GROUP BY department_id ;

#②连接①结果集和employees表，进行筛选
SELECT 
    employee_id,
    last_name,
    salary,
    e.department_id 
FROM
    employees e 
    INNER JOIN 
        (SELECT 
            AVG(salary) ag,
            department_id 
        FROM
            employees 
        GROUP BY department_id) ag_dep 
        ON e.department_id = ag_dep.department_id 
WHERE salary > ag_dep.ag ;

#4.	查询和姓名中包含字母u的员工在相同部门的员工的员工号和姓名
#①查询姓名中包含字母u的员工的部门
SELECT DISTINCT 
    department_id 
FROM
    employees 
WHERE last_name LIKE '%u%' ;

#②查询部门号=①中的任意一个的员工号和姓名
SELECT 
    last_name,
    employee_id 
FROM
    employees 
WHERE department_id IN 
    (SELECT DISTINCT 
        department_id 
    FROM
        employees 
    WHERE last_name LIKE '%u%') ;

#5. 查询在部门的location_id为1700的部门工作的员工的员工号
#①查询location_id为1700的部门
SELECT DISTINCT 
    department_id 
FROM
    departments 
WHERE location_id = 1700 ;

#②查询部门号=①中的任意一个的员工号
SELECT 
    employee_id 
FROM
    employees 
WHERE department_id = ANY 
    (SELECT DISTINCT 
        department_id 
    FROM
        departments 
    WHERE location_id = 1700) ;

#6.查询管理者是King的员工姓名和工资
#①查询姓名为king的员工编号
SELECT 
    employee_id 
FROM
    employees 
WHERE last_name = 'K_ing' ;

#②查询哪个员工的manager_id = ①
SELECT 
    last_name,
    salary 
FROM
    employees 
WHERE manager_id IN 
    (SELECT 
        employee_id 
    FROM
        employees 
    WHERE last_name = 'K_ing') ;

#7.查询工资最高的员工的姓名，要求first_name和last_name显示为一列，列名为 姓.名
#①查询最高工资
SELECT 
    MAX(salary) 
FROM
    employees ;

#②查询工资=①的姓.名
SELECT 
    CONCAT(first_name, last_name) "姓.名" 
FROM
    employees 
WHERE salary = 
    (SELECT 
        MAX(salary) 
    FROM
        employees) ;

多行操作符	含义
in/not in	等于列表中的任意一个
any|some	和子查询返回的某一个值比较
all	和子查询返回的所有值比较

进阶8：分页查询

/*
应用场景：当要显示的数据，一页显示不全，需要分页提交sql请求
语法：
	select 查询列表
	from 表
	【join type join 表2
	on 连接条件
	where 筛选条件
	group by 分组字段
	having 分组后的筛选
	order by 排序的字段】
	limit 【offset,】size;
	
	offset要显示条目的起始索引（起始索引从0开始，为0可省）
	size 要显示的条目个数
特点：
	①limit语句放在查询语句的最后
	②公式
	要显示的页数 page，每页的条目数size
	
	select 查询列表
	from 表
	limit (page-1)*size,size;
	
	size=10
	page  
	1	0
	2  	10
	3	20
*/

分页查询详解

#案例1：查询前五条员工信息
SELECT 
    * 
FROM
    employees 
LIMIT 0, 5 ;

SELECT 
    * 
FROM
    employees 
LIMIT 5 ;

#案例2：查询第11条——第25条
SELECT 
    * 
FROM
    employees 
LIMIT 10, 15 ;

#案例3：有奖金的员工信息，并且工资较高的前10名显示出来
SELECT 
    * 
FROM
    employees 
WHERE commission_pct IS NOT NULL 
ORDER BY salary DESC 
LIMIT 10 ;