一对多或者称为多对一
三张表：出版社，作者信息，书
一对多：一个出版社可以出版多本书
"""
create table books(id int primary key auto_increment,
name char(15) not null,
auther char(15) not null);
create table publisher(id int primary key auto_increment,
name char(15) not null,
book_id int,
foreign key (book_id) references books (id) on update cascade
);
create table students(id int primary key auto_increment,
name char(15) not null,cls_id int,
foreign key (cls_id) references cls (id)
on update cascade on delete cascade);
create table cls(id int primary key auto_increment,
name char(15) not null
);
insert into book(name) values
('九阳神功'),
('九阴真经'),
('九阴白骨爪'),
('独孤九剑'),
('降龙十巴掌'),
('葵花宝典')
;
insert into author_book(author_id,book_id) values
(1,1),
(1,2),
(1,3),
(1,4),
(1,5),
(1,6),
(2,1),
(2,6),
(3,4),
(3,5),
(3,6),
(4,1)
;
"""
import time
from multiprocessing import Process
def task(name):
print(name)
if name=='main':
for i in range(10):
Process(target=task,args=(i,)).start() # 有几率不按顺序打印 证明并发
import time
from threading import Thread,current_thread,enumerate,active_count
def func(i):
time.sleep(1)
# print(i)
# print(current_thread().ident)
# for i in range(10):
# Thread(target=func,args=(i,)).start()
t = Thread(target=func,args=(1,))
t.start()
t.daemon = True
# print(t.ident)
# print(enumerate()) # [<_MainThread(MainThread, started 140735762297728)>, <Thread(Thread-1, started 123145353879552)>]
time.sleep(1) # 这个加了后active_count()结果就是1.
print(active_count())
from multiprocessing import Queue
import queue
q = queue.Queue(4) # 先进先出
q.put(1)
q.put(2)
q.put(3)
print(q.get())
import asyncio
async def func():
print('start time')
await asyncio.sleep(1)
print('end time')
loop = asyncio.get_event_loop()
loop.run_until_complete(func())
import asyncio
async def func():
print(1111)
await asyncio.sleep(1)
print(222)
loop = asyncio.get_event_loop()
loop.run_until_complete(func())
from gevent import monkey
monkey.patch_all()
并发的单例
class A:
from threading import Lock
import time
__instance = None
lock = Lock()
def new(cls, *args, **kwargs):
with cls.lock:
if not cls.__instance:
cls.time.sleep(0.000001)
cls.__instance = super().new(cls)
return cls.__instance
import time
import random
from multiprocessing import Process
def work(dic):
dic['count'] -=1
print(dic)
if name == 'main':
dic={'count':100}
for i in range(100):
p = Process(target=work,args=(dic,))
p.start()
time.sleep(3)
print('---->',dic)