数据库
概念
分类
Oracle
Mysql
去IOE
NoSQL
数据库流行度排名
MYSQL
安装
SQL语句
DCL
DDL
删除用户
创建数据库
删除数据库
创建表
DESC
练习
PRIMARY KEY主键
索引Index
约束Constraint
PRIMARY KEY约束
外键约束Foreign key
视图
数据类型
MYSQL中的数据类型
关系操作
DML---CRUD增删改查
Insert语句
Update语句
Delete语句
Select语句
查询
Limit子句
Where子句
Order by子句
DISTINCT不返回重复记录
聚合函数
分组查询
子查询
连接Join
内连接
外连接
自连接
事务Transaction
原子性：要求事务中的所有操作不可分割，不能做了一部分操作，还剩下一部分；
一致性：多个事务并行执行的结果，应该和事务排队执行的结果一致。如果事务的并行执行和多线程读写共享资源一样不可预期，就不能保证一致性；
隔离性，就是指多个事务访问共同的数据了，应该互不干扰。隔离性指的是究竟在一个事物处理期间，其他事务能不能访问的问题；
持久性：比较好理解，就是事务提交后，数据不能丢失。
MYSQL隔离级别
事务语法
数据仓库和数据库的区别
其他概念
游标Cursor
存储过程、触发器
数据库开发
驱动
pymysql使用
$pip install pymysql
创建数据库和表
CREATE DATABASE IF NOT EXISTS school; SHOW DATABASES; USE school;
CREATE TABLE `student` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, `age` int(11) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
连接Connect
import pymysql conn = None try: #建立连接 conn = pymysql.connect('192.168.10.166','wayne','wayne','test') print(conn.ping(False)) finally: if conn: conn.close()
游标Cursor
操作数据库
新增记录
import pymysql conn = None try: #建立连接 conn = pymysql.connect('192.168.10.166','wayne','wayne','school') print(conn.ping(False)) #获取游标 cursor = conn.cursor() insert_sql = "insert into student (id,name,age) values(10,'tom',20)" rows = cursor.execute(insert_sql) print(rows) cursor.close() finally: if conn: conn.close()
事务管理
import pymysql conn = None cursor = None try: conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor() insert_sql = "insert into student (name,age) values('tom',21)" rows = cursor.execute(insert_sql) print(rows) conn.commit() except: conn.rollback() finally: if cursor: cursor.close() if conn: conn.close()
批量增加数据
import pymysql conn = None cursor = None try: conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor() for i in range(5): insert_sql = "insert into student (name,age) values('tom',21)" rows = cursor.execute(insert_sql) conn.commit() except: conn.rollback() finally: if cursor: cursor.close() if conn: conn.close()
一般流程
查询
import pymysql conn = None cursor = None try: conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor() sql = "select * from student" rows = cursor.execute(sql) #返回影响行数 print(cursor.fetchone()) print(cursor.fetchmany(2)) print(cursor.fetchall()) except: pass finally: if cursor: cursor.close() if conn: conn.close()
带列名查询
import pymysql from pymysql.cursors import DictCursor conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor(DictCursor) sql = "select * from student" rows = cursor.execute(sql) print(cursor.fetchone())#{'id': 1, 'name': 'tom', 'age': 20} print(cursor.fetchall())#[{'id': 2, 'name': 'tom', 'age': 21}]
SQL注入攻击
#找出用户id为5的用户信息语句如下： import pymysql conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor() userid = '5' sql = 'select * from student where id = {}'.format(userid) cursor.execute(sql) print(cursor.fetchall()) #((5, 'zqk', 23),)
#userid可以变，例如从客户端request请求中获取，直接拼接到查询字符串中 #当userid='5 or 1=1'呢？ import pymysql conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor() userid = '5 or 1=1' sql = 'select * from student where id = {}'.format(userid) cursor.execute(sql) print(cursor.fetchall()) #((1, 'tom', 20), (2, 'tom', 21), (3, 'cy', 22), (4, 'xu', 24), (5, 'zqk', 23)) #运行结果返回了数据库全部数据
import pymysql conn = pymysql.connect('192.168.10.166','wayne','wayne','school') cursor = conn.cursor() userid = '5 or 1=1' sql1 = 'SELECT * FROM student WHERE id = %s' cursor.execute(sql1,(userid,)) #参数化查询 print(cursor.fetchall()) print('~~~~~~~~~~~~~~') sql2 = "SELECT * FROM student WHERE name like %(name)s and %(age)s" #参数化查询 cursor.execute(sql2,{'name':'tom','age':19}) print(cursor.fetchall()) if cursor: cursor.close() if conn: conn.close() #运行结果如下： D:Anaconda3libsite-packagespymysqlcursors.py:166: Warning: (1292, "Truncated incorrect DOUBLE value: '5 or 1=1'") result = self._query(query) ((5, 'zqk', 23),) ~~~~~~~~~~~~~~ ((1, 'tom', 20), (2, 'tom', 21))
参数化查询为什么提高效率？
上下文支持
查看连接类和游标类的源码
#连接类 class Connection(object): def __enter__(self): """Context manager that returns a Cursor""" return self.cursor() def __exit__(self, exc, value, traceback): """On successful exit, commit. On exception, rollback""" if exc: self.rollback() else: self.commit()
#游标类 class Cursor(object): def __enter__(self): """Context manager that returns a Cursor""" return self.cursor() def __exit__(self, exc, value, traceback): """On successful exit, commit. On exception, rollback""" if exc: self.rollback() else: self.commit()
#使用游标的上下文 import pymysql conn = pymysql.connect('192.168.10.166','wayne','wayne','school') try: with conn.cursor() as cursor: for i in range(3): insert_sql = "insert into student (name,age) values('tom{0}',21+{0})".format(i) rows = cursor.execute(insert_sql) conn.commit() #此时使用这个关闭的cursor，会抛异常 # sql = "select * from student" # cursor.execute(sql) # print(cursor.fetchall()) except Exception as e: print(e) conn.rollback() finally: conn.close()
#使用连接的上下文 import pymysql conn = pymysql.connect('192.168.10.166','wayne','wayne','school') with conn as cursor: for i in range(3): insert_sql = "insert into student (name,age) values('tom{0}',21+{0})".format(i) rows = cursor.execute(insert_sql) sql = "select * from student" cursor.execute(sql) print(cursor.fetchall()) #关闭 cursor.close() conn.close()
#同时使用连接类和游标类的上下文管理 import pymysql conn = pymysql.connect('192.168.10.166','wayne','wayne','school') with conn as cursor: with cursor: sql = "select * from student" cursor.execute(sql) print(cursor.fetchall()) #关闭 conn.close()
连接池的实现
from queue import Queue import pymysql class ConnPool: def __init__(self,size,*args,**kwargs): if not isinstance(size,int)or size<1: size = 8 self._pool = Queue(size) for i in range(size): self._pool.put(pymysql.connect(*args,**kwargs)) def get_conn(self): return self._pool.get() #阻塞 def return_conn(self,conn): self._pool.put(conn) #使用连接池 pool = ConnPool(4,'192.168.10.166','wayne','wayne','school') #获取一个连接 conn = pool.get_conn() with conn as cursor: with cursor: sql = "SELECT * FROM student" cursor.execute(sql) print(cursor.fetchone()) sql = "SHOW PROCESSLIST" #观察连接，权限小只能看自己的 cursor.execute(sql) for x in cursor: print(x) #归还连接 pool.return_conn(conn)
class ConnPool: def __enter__(self): return self.get_conn() def __exit__(self, exc_type, exc_val, exc_tb): #归还谁呢？ pass
from queue import Queue import pymysql import threading class ConnPool: def __init__(self,size,*args,**kwargs): if not isinstance(size,int)or size<1: size = 8 self._pool = Queue(size) for i in range(size): self._pool.put(pymysql.connect(*args,**kwargs)) self.local = threading.local() def get_conn(self): return self._pool.get() #阻塞 def return_conn(self,conn): self._pool.put(conn) def __enter__(self): #self.local.conn在当前线程不存在抛属性异常 if getattr(self.local,'conn',None) is None: self.local.conn = self.get_conn() return self.local.conn.cursor() #返回一个游标 def __exit__(self, exc_type, exc_val, exc_tb): if exc_type: self.local.conn.rollback() else: self.local.conm.commit() self.return_conn(self.local.conn) self.local.conn = None #使用连接池 pool = ConnPool(4,'192.168.10.166','wayne','wayne','school') #获取一个连接 conn = pool.get_conn() with conn as cursor: #自动拿连接并归还，还自动提交和回滚 with cursor: sql = "SELECT * FROM student" cursor.execute(sql) print(cursor.fetchone()) sql = "SHOW PROCESSLIST" #观察连接，权限小只能看自己的 cursor.execute(sql) for x in cursor: #对结果记录进行迭代 print(x)
with conn as cursor:
with cursor:
threading.Thread(target=xxx,args=(cursor,))
