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
支持标量子查询 （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：
-子查询放在小括号内
-子查询一般放在条件的右侧
-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
-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
#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的结果
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
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、查询公司的最低公司
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)
from employees
GROUP BU department_id
#3、在2基础上筛选，满足min(salary) > 1
select min(salary)
from employees
GROUP BU department_id
having min(salary)(
select min(salary)
from employees
where department_id = 50
)
#非法使用标量子查询，子查询的结果不是一行一列
select min(salary)
from employees
GROUP BU department_id
having min(salary)(
select salary
from employees
where department_id = 50
)
#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 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、返回其他工种中比job_id为‘IT_PROG’工种任一工资低的员工的工号、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、查询员工的工号、姓名、job_id以及salary，salary 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：返回其他工种中比job_id为‘IT_PROG’工种所有工资低的员工的工号、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，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) = ( 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 #案例二：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 ) #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 selec AVG(salary), department_id from employees GROUP BY department_id #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 ( selec 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或者0 */ select EXISTS(select employee_id from employees where salary = 30000) #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 epartment_name from departments 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 ) #练习 #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 departmetn_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 departmetn_id from employees where last_name = 'zlotkey' ) #2.查询工资比公司平均工资搞的员工的员工号、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, employees_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搞的员工的员工号，姓名和工资 #1.查询各部门的评平均工资 select AVG(salary), department_id from employees GROUP BY department_id #2.连接1结果集和employees表 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、查询姓名中包含字母u的员工在相同部门的员工号和姓名 #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.查询在部门的location_id 为1700的部门 select departmetn_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 departmetn_id = ANY ( select departmetn_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frist_name和last_naem 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 employess where salary = ( select MAX(salary) from employees ) #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 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） size 要显示的条目个数 特点： -limit语句放在查询语句的最后 -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 */ #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 #作业 #1、查询工资最低的员工信息 #1.查询最低的工资 select MIN(salary) from employees #2.查询last_name, salary要求salary=1 select last_name, salary from employees where salary = ( select MIN(salary) from employees ) #2、查询平均工资最低的部门信息 #方式一 #1.各部门的平均工资 select AVG(salary), department_id from employees GROPU BY ddepartment_id #2.查询1结果上的最低平均工资 select MIN(ag) from ( select AVG(salary) ag , department_id from employees GROPU BY ddepartment_id ) ag_dep #3.查询哪个部门的平均工资=2 select AVG(salary), department_id from employees GROPU BY ddepartment_id having AVG(salary) = ( select MIN(ag) from ( select AVG(salary) ag , department_id from employees GROPU BY ddepartment_id ) ag_dep ) #4.查询部门信息 select d.* from departments d where d.department_id = ( select department_id from employees GROPU BY ddepartment_id having AVG(salary) = ( select MIN(ag) from ( select AVG(salary) ag , department_id from employees GROPU BY ddepartment_id ) ag_dep ) ) #方式二 #1.各部门的平均工资 select AVG(salary), department_id from employees GROPU BY ddepartment_id #2.求出最低平均工资的部门编号 select AVG(salary), department_id from employees GROPU BY ddepartment_id ORDER BY AVG(salary) LIMIT 1 #.3.查询部门信息 select * from departments where = department_id = ( select AVG(salary), department_id from employees GROPU BY ddepartment_id ORDER BYAVG(salary) LIMIT 1 ) #3、查询平均工资最低的部门信息和该部门的平均工资 #1.各部门的平均工资 select AVG(salary), department_id from employees GROPU BY ddepartment_id #2.求出最低平均工资的部门编号 select AVG(salary), department_id from employees GROPU BY ddepartment_id ORDER BY AVG(salary) LIMIT 1 #3.查询部门信息 select d.*, ag from departments d join ( select AVG(salary), department_id from employees GROPU BY ddepartment_id ORDER BY AVG(salary) LIMIT 1 ) ag_dep ON d.department_id = ag_dep.department_id #4、查询平均工资最高job信息 #1.查询每个job的平均工资 select AVG(salary), job_id from employees GROUP BY job_id ORDER BY AVG(salary) DESC LIMIT 1 #2.查询job信息 select * from jobs where job_id = ( select job_id from employees GROUP BY job_id ORDER BY AVG(salary) DESC LIMIT 1 ) #5、查询平均工资高于公司平均工资的部门有哪些 #1.查询平均工资 select AVG(salary) from employees #2.查询每个部门的平均工资 select AVG(salary), department_id from employees GROUP BY department_id #3.筛选2结果集，满足平均工资>1 select AVG(salary), department_id from employees GROUP BY department_id HAVING AVG(salary) ( select AVG(salary) from employees ) #6、查询出公司中所有manager的详细信息 #1.查询所有manage的员工编号 select DISTINCT manager_id from employees #2.查询详细信息，满足employe_id=1 select * from employees where employee_id = ANY ( select DISTINCT manager_id from employees ) #7、各个部门中，最高工资中最低的那个部门的最低工资是多少 #1.查询各部门的最高工资中最低的部门编号 select department_id from employees GROUP BY department_id ORDER BY MAX(salary) LIMIT 1 #2.查询1结果的那个部门的最低工资 select MAX(salary), departmetn_id from employees where department_id = ( select department_id from employees GROUP BY department_id ORDER BY MAX(salary) LIMIT 1 ) #8、查询平均工资最高的部门的manage的详细信息:last_name, departmetn_id, email, salary #1.查询平均工资最高的部门编号 select department_id FROM employees GROUP BY department_id ORDER BY AVG(salary) DESC LIMIT 1 #2.讲employees和departments连接查询，筛选条件是1 select last_name, d.departmetn_id, email, salary from employees e INNER JOIN departments d ON d.manager_id = e.employee_id where d.department_id = ( select department_id FROM employees GROUP BY department_id ORDER BY AVG(salary) DESC LIMIT ) #进阶9：联合查询 /* union 联合 合并：讲多条查询语句的结果合并成一个结果 语法： 查询语句1 union 查询语句2 union ... 应用场景： 要查询的结果来自于多个表，且多个表没有直接的连接关系，但查询的信息一致时 特点： 1、要求多条查询语句的查询列表数一致的 2、要求多条查询语句的查询的每一列的类型和顺序最好一致 3、union关键字默认去重，如果使用union all 可以包含重复项 */ # 引入的案例：查询部门编号>90或邮箱中包含a的员工信息 select * from employees where email LIKE '%a%' OR department_id > 90; select * from employees where email LIKE '%a%' UNION select * from employees wheredepartment_id > 90; #案例：查询中国用户中性别=男的信息以及外国用户中性别=男的用户信息 select id, cname, csex from t_ca where csex = '男' UNION ALL select t_id, tName, tGender from t_ua where tGender = 'male' 语法： select 查询列表 7 from 表1 别名 1 连接类型 join 表2 2 on 连接条件 3 where 筛选 4 group by 分组列表 5 having 筛选 6 order by 排序列表 8 limit 其实条目索引，条目数 9