mysql基本指令2

pymysql:
  - 连接、关闭（游标）
  - execute()   -- SQL注入    sss' or 1=1 --
  - 增删改： conn.commit()
  - fetchone fetchall
  - 获取插入数据自增ID

转储SQL文件
 命令行：
  mysqldump
  
  数据备份: 数据表结构+数据
   mysqldump -u 用户名  已有的数据库名 > 要转成的数据库名 -p
  
  数据备份：数据表结构
   mysqldump -u root -d db1 > db1.sql -p
   
  导入数据库：
   create database XX；
   mysqldump -u root -d XX < db1.sql -p
   

# 查询课程大于60   
-- select * from score where num>60;
# 查询课程
-- select *from course;
# 查询任课老师
-- select * from course left join teacher no course.teacher_id = teacher.id;
# 查询学生对应的班级
-- select * from student left join class on student.class_id = class.id;
# 统计学生性别人数
-- select gender count(nid) from  sudent GROUP BY gender;

临时表:
 select num, course_id from (select num , course_id from score where num > 60) as B
 
 
 
 
 
查：
 in not in
 between and
 limit
 group by
 order by
 like "%a"
 left join xx on
 临时表：
  select * from (select * from tb where id < 10) as B
 
 select id,name,1,(select count(1) from tb) from tb2;
  
 select
  student_id ,
  select num from score as s2 where s2.student_id=s1.student_id and course_id= 1) as 语文,
  select num from score as s2 where s2.student_id = s1.student_id and course_id = 2) as 数学,
  select num from score as s2 where s2.student_id = s1.student_id and course_id = 3) as 英语
 from score as s1;