day 46子查询（in all any exists）

上节课复习：
1、内链接
select * from 左表 inner join 右表 on 左表.字段 = 右表.字段;
2、左链接
select * from 左表 left join 右表 on 左表.字段 = 右表.字段;
3、右链接
select * from 左表 right join 右表 on 左表.字段 = 右表.字段;
4、全外链接
select * from 左表 left join 右表 on 左表.字段 = 右表.字段;
union
select * from 左表 right join 右表 on 左表.字段 = 右表.字段;

今日内容：
1、子查询
2、pymysql
3、视图、触发器、事务、存储过程、内置函数、流程控制
4、索引

1.子查询

# 1、in
select * from emp where age=18 or age=38 or age=28;
select * from emp where age in (18,38,28);

# 子查询的思路
select * from emp where dep_id in
(select id from dep where name="技术" or name="销售");

# 链表的思路
select * from emp inner join dep
on emp.dep_id = dep.id
where dep.name in ("技术","销售");


# not in不支持null
mysql> select * from dep;
+------+--------------+
| id   | name         |
+------+--------------+
|  200 | 技术         |
|  201 | 人力资源     |
|  202 | 销售         |
|  203 | 运营         |
+------+--------------+
4 rows in set (0.00 sec)
mysql> insert into emp values(7,'lili','female',48,null);
Query OK, 1 row affected (0.03 sec)

mysql> select * from emp
    -> ;
+----+------------+--------+------+--------+
| id | name       | sex    | age  | dep_id |
+----+------------+--------+------+--------+
|  1 | egon       | male   |   18 |    200 |
|  2 | alex       | female |   48 |    201 |
|  3 | wupeiqi    | male   |   38 |    201 |
|  4 | yuanhao    | female |   28 |    202 |
|  5 | liwenzhou  | male   |   18 |    200 |
|  6 | jingliyang | female |   18 |    204 |
|  7 | lili       | female |   48 |   NULL |
+----+------------+--------+------+--------+
7 rows in set (0.00 sec)

mysql>


查询出有员工的部门，
select * from dep where id in
(select distinct dep_id from emp);

查询出没有员工的部门，
select * from dep where id not in
(select distinct dep_id from emp);


select * from dep where id not in
(select distinct dep_id from emp where dep_id is not null);

2.any和all

 any后也跟子查询语句，与in不一样的地方在哪里
   in (子查询语句)
   in (值1,值2,值3)
   而any只能跟子查询语句
   any必须跟比较运算符配合使用


select * from emp where dep_id in
(select id from dep where name in ("技术","人力资源"));

select * from emp where dep_id = any
(select id from dep where name in ("技术","人力资源"));


select * from emp where dep_id not in
(select id from dep where name in ("技术","人力资源"));

select * from emp where ! (dep_id = any(select id from dep where name in ("技术","人力资源")));


查询出那些薪资比所有部门的平均薪资都高的员工=》薪资在所有部门平均线以上的狗币资本家
select * from employee where salary > all
(select avg(salary) from employee where depart_id is not null group by depart_id);

查询出那些薪资比所有部门的平均薪资都低的员工=》薪资在所有部门平均线以下的无产阶级劳苦大众
select * from employee where salary < all
(select avg(salary) from employee where depart_id is not null group by depart_id);

查询出那些薪资比任意一个部门的平均薪资高的员工=》薪资在任一部门平均线以上的员工
select * from employee where salary > any
(select avg(salary) from employee where depart_id is not null group by depart_id);


select * from employee where salary < any
(select avg(salary) from employee where depart_id is not null group by depart_id);

3.子查询exists

# exists  vs in
# in的效果 高于 exists
# 见博客：https://www.cnblogs.com/linhaifeng/articles/7267596.html#_label4

select * from 表1 where exists (select * from 表2);

# 例如：查询有员工的部门=》
select * from dep where exists (select * from emp where dep.id=emp.dep_id);


# not exists的效果 高于 not in
select * from dep where not exists (select * from emp where 203=emp.dep_id);



# 例：查询选修了所有课程的学生id、name:

# 实现方式一：选修了三门课程的学生就是选修了所有课程的学生
select s.id,s.name from student as s inner join student2course as sc
on s.id = sc.sid
group by sc.sid
having count(sc.cid) = (select count(id) from course);

# 实现方式二：找到这样的学生，该学生不存在没有选修过的课程
select * from student as s where not exists (
    select * from course as c not exists (
        select * from student2course as sc where sc.sid = s.id and sc.cid = c.id
    )
);


select * from student as s where not exists (
    select * from course as c where not exists (
        select * from student2course as sc where sc.sid = s.id and sc.cid = c.id
    )
);



学生记录可以过滤出来，一定是子查询内没有记录

for 学生: # s.id=2
    for 课程: # c.id=1
        for 学生2课程: # sc.sid = 2 and sc.cid = 1
            pass

==================================
for sid in [1,2,3,4]:
    for cid in [1,2,3]:
        (sid,cid)


最外层循环一次
# (1,1)
# (1,2)
# (1,3)
最外层循环二次
# (2,1)
# (2,2)
# (2,3)
最外层循环三次
# (3,1)
# (3,2)
# (3,3)
最外层循环四次
# (4,1)
# (4,2)
# (4,3)

===================================
# 例2、查询没有选择所有课程的学生，即没有全选的学生。=》找出这样的学生，存在没有选修过的课程
select * from student as s where exists (
    select * from course as c where not exists (
        select * from student2course as sc where sc.sid = s.id and sc.cid = c.id
    )
);

# 例3、查询一门课也没有选的学生=》找出这样的学生，不存在选修过的课程
select * from student as s where not exists (
    select * from course as c where exists (
        select * from student2course as sc where sc.sid = s.id and sc.cid = c.id
    )
);

# 例4、查询至少选修了一门课程的学生=》找出这样的学生，存在选修过课程
select * from student as s where exists (
    select * from course as c where exists (
        select * from student2course as sc where sc.sid = s.id and sc.cid = c.id
    )
);

4.pymysql

import pymysql  # pip3 install pymysql

conn = pymysql.connect(host="127.0.0.1", port=3306, user="root", password="123", db="db13", charset="utf8mb4")
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)

# 记录=》增删改
# cursor.execute("insert into student values(%s,%s)",[5,'kkk'])
# cursor.executemany("insert into student values(%s,%s)",[(6,'xxx'),(7,'yyy'),(8,'zzzz')])

cursor.execute("insert into student(name) values(%s)",['zzz'])
print(cursor.lastrowid)

# cursor.execute("delete from student where id > 6;")

# 记录=》查
# rows = cursor.execute('select * from student;')
# print(rows)

# line = cursor.fetchone()
# print(line)
# line = cursor.fetchone()
# print(line)
#
# lines = cursor.fetchmany(2)
# print(lines)
# lines = cursor.fetchall()
# print(lines)

# for line in cursor:
#     print(line)


# cursor.scroll(3,mode='absolute')  # 相对绝对位置移动
# print(cursor.fetchone())
# print(cursor.fetchall())
# cursor.scroll(0,mode='absolute')  # 相对绝对位置移动
# print(cursor.fetchall())


# cursor.fetchone()
# cursor.scroll(1,mode='relative') # 相对当前位置移动
# cursor.scroll(0,mode='absolute') # 相对当前位置移动
# print(cursor.fetchone())

conn.commit()
cursor.close()
conn.close()