下载        http://dev.mysql.com/downloads/mysql/安装        windows:            点点点        Linux:            yum install mysql-server        Mac:            点点点

SHOW DATABASES;

USE db_name;

SHOW TABLES;

创建用户    create user ‘用户名‘@‘IP地址‘ identified by ‘密码‘;删除用户    drop user ‘用户名‘@‘IP地址‘;修改用户    rename user ‘用户名‘@‘IP地址‘; to ‘新用户名‘@‘IP地址‘;;修改密码    set password for ‘用户名‘@‘IP地址‘ = Password(‘新密码‘) PS：用户权限相关数据保存在mysql数据库的user表中，所以也可以直接对其进行操作（不建议）

show grants for ‘用户‘@‘IP地址‘                                     -- 查看权限grant  权限 on 数据库.表 to   ‘用户‘@‘IP地址‘ identified by ‘密码‘     -- 授权并创建密码revoke 权限 on 数据库.表 from ‘用户‘@‘IP地址‘                         -- 取消权限

all privileges  除grant外的所有权限select          仅查权限select,insert   查和插入权限...usage                   无访问权限alter                   使用alter tablealter routine           使用alter procedure和drop procedurecreate                  使用create tablecreate routine          使用create procedurecreate temporary tables 使用create temporary tablescreate user             使用create user、drop user、rename user和revoke  all privilegescreate view             使用create viewdelete                  使用deletedrop                    使用drop tableexecute                 使用call和存储过程file                    使用select into outfile 和 load data infilegrant option            使用grant 和 revokeindex                   使用indexinsert                  使用insertlock tables             使用lock tableprocess                 使用show full processlistselect                  使用selectshow databases          使用show databasesshow view               使用show viewupdate                  使用updatereload                  使用flushshutdown                使用mysqladmin shutdown(关闭MySQL)super                   使用change master、kill、logs、purge、master和set global。还允许mysqladmin调试登陆replication client      服务器位置的访问replication slave       由复制从属使用

对于目标数据库以及内部其他：    数据库名.*           数据库中的所有    数据库名.表          指定数据库中的某张表    数据库名.存储过程     指定数据库中的存储过程    *.*                所有数据库

用户名@IP地址         用户只能在改IP下才能访问用户名@192.168.1.%   用户只能在改IP段下才能访问(通配符%表示任意)用户名@%             用户可以再任意IP下访问(默认IP地址为%)

create table 表名(    列名  类型  是否可以为空，    列名  类型  是否可以为空)

是否可空，null表示空，非字符串    not null    - 不可空    null        - 可空

默认值，创建列时可以指定默认值，当插入数据时如果未主动设置，则自动添加默认值    create table tb1(        nid int not null defalut 2,        num int not null    )

自增，如果为某列设置自增列，插入数据时无需设置此列，默认将自增（表中只能有一个自增列）    create table tb1(        nid int not null auto_increment primary key,        num int null    )    或    create table tb1(        nid int not null auto_increment,        num int null,        index(nid)    )    注意：1、对于自增列，必须是索引（含主键）。         2、对于自增可以设置步长和起始值             show session variables like ‘auto_inc%‘;             set session auto_increment_increment=2;             set session auto_increment_offset=10;             shwo global  variables like ‘auto_inc%‘;             set global auto_increment_increment=2;             set global auto_increment_offset=10;

主键，一种特殊的唯一索引，不允许有空值，如果主键使用单个列，则它的值必须唯一，如果是多列，则其组合必须唯一。    create table tb1(        nid int not null auto_increment primary key,        num int null    )    或    create table tb1(        nid int not null,        num int not null,        primary key(nid,num)    )

    create table tb1(        nid int not null auto_increment primary key,        num int null unique key,    )

外键，一个特殊的索引，只能是指定内容    creat table color(        nid int not null primary key,        name char(16) not null    )    create table fruit(        nid int not null primary key,        smt char(32) null ,        color_id int not null,        constraint fk_cc foreign key (color_id) references color(nid)    )

drop table 表名

delete from 表名truncate table 表名  # 和上面的区别在于，这条语句能够使自增id恢复到0

添加列：alter table 表名 add 列名 类型删除列：alter table 表名 drop column 列名修改列：        alter table 表名 modify column 列名 类型;  -- 类型        alter table 表名 change 原列名 新列名 类型; -- 列名，类型 添加主键：        alter table 表名 add primary key(列名);删除主键：        alter table 表名 drop primary key;        alter table 表名  modify  列名 int, drop primary key; 添加外键：alter table 从表 add constraint 外键名称（形如：FK_从表_主表） foreign key 从表(外键字段) references 主表(主键字段);删除外键：alter table 表名 drop foreign key 外键名称 修改默认值：ALTER TABLE testalter_tbl ALTER i SET DEFAULT 1000;删除默认值：ALTER TABLE testalter_tbl ALTER i DROP DEFAULT;

insert into 表 (列名,列名...) values (值,值,值...)insert into 表 (列名,列名...) values (值,值,值...),(值,值,值...)insert into 表 (列名,列名...) select (列名,列名...) from 表

delete from 表delete from 表 where id＝1 and name＝‘alex‘

update 表 set name ＝ ‘alex‘ where id>1

select * from 表select * from 表 where id > 1select nid,name,gender as gg from 表 where id > 1

1、条件    select * from 表 where id > 1 and name != ‘alex‘ and num = 12;    select * from 表 where id between 5 and 16;    select * from 表 where id in (11,22,33)    select * from 表 where id not in (11,22,33)    select * from 表 where id in (select nid from 表)2、通配符    select * from 表 where name like ‘ale%‘  - ale开头的所有（多个字符串）    select * from 表 where name like ‘ale_‘  - ale开头的所有（一个字符）3、限制    select * from 表 limit 5;            - 前5行    select * from 表 limit 4,5;          - 从第4行开始的5行    select * from 表 limit 5 offset 4    - 从第4行开始的5行4、排序    select * from 表 order by 列 asc              - 根据 “列” 从小到大排列    select * from 表 order by 列 desc             - 根据 “列” 从大到小排列    select * from 表 order by 列1 desc,列2 asc    - 根据 “列1” 从大到小排列，如果相同则按列2从小到大排序5、分组    select num from 表 group by num    select num,nid from 表 group by num,nid    select num,nid from 表  where nid > 10 group by num,nid order nid desc    select num,nid,count(*),sum(score),max(score),min(score) from 表 group by num,nid    select num from 表 group by num having max(id) > 10    特别的：group by 必须在where之后，order by之前6、连表    无对应关系则不显示    select A.num, A.name, B.name    from A,B    Where A.nid = B.nid    无对应关系则不显示    select A.num, A.name, B.name    from A inner join B    on A.nid = B.nid    A表所有显示，如果B中无对应关系，则值为null    select A.num, A.name, B.name    from A left join B    on A.nid = B.nid    B表所有显示，如果B中无对应关系，则值为null    select A.num, A.name, B.name    from A right join B    on A.nid = B.nid7、组合    组合，自动处理重合    select nickname    from A    union    select name    from B    组合，不处理重合    select nickname    from A    union all    select name    from B

pip install pymysql

# 先往数据库插入点数据mysql> CREATE DATABASE IF NOT EXISTS testdb DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;mysql> use testdb;mysql> CREATE TABLE hosts (id int not null auto_increment primary key,ip varchar(20) not null,port int not null);mysql> INSERT INTO hosts (ip,port) values        (‘1.1.1.1‘,22),(‘1.1.1.2‘,22),       (‘1.1.1.3‘,22),(‘1.1.1.4‘,22),       (‘1.1.1.5‘,22);

#!/usr/bin/env python# -*- coding:utf-8 -*-import pymysql# 创建连接conn = pymysql.connect(host=‘127.0.0.1‘, port=3306, user=‘root‘, passwd=‘123456‘, db=‘testdb‘)# 创建游标cursor = conn.cursor()# 执行SQL，并返回收影响行数r = effect_row = cursor.execute("update hosts set ip = ‘1.1.1.2‘")print(r)# 执行SQL，并返回受影响行数effect_row = cursor.execute("update hosts set ip = ‘1.1.1.6‘ where id > %s", (6,))# 执行SQL，并返回受影响行数effect_row = cursor.executemany("insert into hosts(ip,port) values(%s,%s)", [("1.1.1.7",21),("1.1.1.8",23)])# 提交，不然无法保存新建或者修改的数据conn.commit()# 关闭游标cursor.close()# 关闭连接conn.close()

#!/usr/bin/env python# -*- coding:utf-8 -*-import pymysqlconn = pymysql.connect(host=‘127.0.0.1‘, port=3306, user=‘root‘, passwd=‘123456‘, db=‘testdb‘)cursor = conn.cursor()cursor.executemany("insert into hosts(ip,port) values(%s,%s)", [("1.1.1.9",21),("1.1.1.10",222)])conn.commit()cursor.close()conn.close()# 获取最新自增IDnew_id = cursor.lastrowidprint(new_id)

# 获取当前行行号
current_row = cursor.rownumber
print(current_row)

#!/usr/bin/env python# -*- coding:utf-8 -*-import pymysqlconn = pymysql.connect(host=‘127.0.0.1‘, port=3306, user=‘root‘, passwd=‘123456‘, db=‘testdb‘)cursor = conn.cursor()cursor.execute("select * from hosts")# 获取第一行数据row = cursor.fetchone()print(row)print(cursor.rownumber)# 获取第二行数据row_1 = cursor.fetchone()print(row_1)print(cursor.rownumber)# 获取前n行数据row_2 = cursor.fetchmany(3)print(row_2)# 获取所有数据row_3 = cursor.fetchall()print(row_3)conn.commit()cursor.close()conn.close()

#!/usr/bin/env python# -*- coding:utf-8 -*-import pymysqlconn = pymysql.connect(host=‘127.0.0.1‘, port=3306, user=‘root‘, passwd=‘123456‘, db=‘testdb‘)# 游标设置为字典类型cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)r = cursor.execute("select * from hosts")print(r)result = cursor.fetchone()print(result)conn.commit()cursor.close()conn.close()

pip install sqlalchemy

MySQL-Python    mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>  pymysql    mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]  MySQL-Connector    mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>  cx_Oracle    oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]  更多详见：http://docs.sqlalchemy.org/en/latest/dialects/index.html

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy import create_engineengine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/testdb", max_overflow=5)  # max_overflow可以超出连接池5个连接#执行SQLcur = engine.execute(    "INSERT INTO hosts (ip,port) VALUES (‘1.1.1.11‘, 22)")#新插入行自增IDcur.lastrowid#执行SQLcur = engine.execute(    "INSERT INTO hosts (ip,port) VALUES(%s, %s)",[(‘1.1.1.12‘, 22),(‘1.1.1.13‘, 55),])#执行SQLcur = engine.execute(    "INSERT INTO hosts (ip,port) VALUES (%(ip)s, %(port)s)",    ip=‘1.1.1.15‘, port=80)#执行SQLcur = engine.execute(‘select * from hosts‘)#获取第一行数据cur.fetchone()#获取第n行数据cur.fetchmany(3)#获取所有数据cur.fetchall()

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom sqlalchemy import create_engineengine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/testdb", max_overflow=5)Base = declarative_base()# 创建单表class Users(Base):    __tablename__ = ‘users‘    id = Column(Integer, primary_key=True,autoincrement=True)     name = Column(String(32))    extra = Column(String(16))    __table_args__ = (    UniqueConstraint(‘id‘, ‘name‘, name=‘uix_id_name‘), # 设置组合唯一键约束        Index(‘ix_id_name‘, ‘name‘, ‘extra‘),     # 创建索引    )# 一对多关系class Favor(Base):    __tablename__ = ‘favor‘    nid = Column(Integer, primary_key=True,autoincrement=True)    caption = Column(String(50), default=‘playing‘, unique=True)class Person(Base):    __tablename__ = ‘person‘    nid = Column(Integer, primary_key=True,autoincrement=True)    name = Column(String(32), index=True, nullable=True)    favor_id = Column(Integer, ForeignKey("favor.nid"))  # 设置外键,外键依赖于主表favor的主键nid    # 与生成表结构无关，仅用于外键查询方便    favor = relationship("Favor", backref=‘pers‘)# 多对多class Group(Base):    __tablename__ = ‘group‘    id = Column(Integer, primary_key=True,autoincrement=True)    name = Column(String(64), unique=True, nullable=False)    # group = relationship(‘Group‘,secondary=ServerToGroup,backref=‘host_list‘)class Server(Base):    __tablename__ = ‘server‘    id = Column(Integer, primary_key=True, autoincrement=True)    hostname = Column(String(64), unique=True, nullable=False)    port = Column(Integer, default=22)class ServerToGroup(Base):    """多对多关系,则是多生成一张表用来存储主键"""    __tablename__ = ‘servertogroup‘    nid = Column(Integer, primary_key=True, autoincrement=True)    server_id = Column(Integer, ForeignKey(‘server.id‘))  # 设置主键    group_id = Column(Integer, ForeignKey(‘group.id‘))    # 设置主键def init_db():    """创建表的函数,调用之后会创建表"""    Base.metadata.create_all(engine)def drop_db():    """删除表的函数,调用之后会删除表"""    Base.metadata.drop_all(engine)init_db() # 创建完最好注释,如果表已经创建,执行此步不会再创建表# drop_db()# 想要对表进行操作则需要绑定会话Session = sessionmaker(bind=engine)session = Session()

# 插入一条obj = Users(name=‘redhat‘, extra=‘rh‘)print(obj)session.add(obj)# 插入多条session.add_all([    Users(name=‘centos‘, extra=‘ct‘),    Users(name=‘debian‘, extra=‘db‘),    Users(name=‘ubuntu‘, extra=‘ub‘),    Users(name=‘fedora‘, extra=‘fd‘),])# 插入完需要提交否则不生效session.commit()

session.query(Users).filter(Users.id > 5).delete()session.commit()

session.query(Users).filter(Users.id > 2).update({"name" : "opensuse"})session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + "099"}, synchronize_session=False)#session.query(Users).filter(Users.id > 2).update({"num": Users.num + 1}, synchronize_session="evaluate") session.commit()

ret = session.query(Users).all()ret = session.query(Users.name, Users.extra).all()ret = session.query(Users).filter_by(name=‘opensuse099‘).all()ret = session.query(Users).filter_by(name=‘opensuse099‘).first()

#　条件ret = session.query(Users).filter_by(name=‘centos‘).all()ret = session.query(Users).filter(Users.id > 1, Users.name == ‘centos‘).all()ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == ‘centos‘).all()ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name=‘centos‘))).all()from sqlalchemy import and_, or_ret = session.query(Users).filter(and_(Users.id > 3, Users.name == ‘centos‘)).all()ret = session.query(Users).filter(or_(Users.id < 2, Users.name == ‘centos‘)).all()ret = session.query(Users).filter(    or_(        Users.id < 2,        and_(Users.name == ‘centos‘, Users.id > 3),        Users.extra != ""    )).all()# 通配符ret = session.query(Users).filter(Users.name.like(‘e%‘)).all()ret = session.query(Users).filter(~Users.name.like(‘e%‘)).all()# 限制ret = session.query(Users)[1:2]# 排序ret = session.query(Users).order_by(Users.name.desc()).all()ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()# 分组from sqlalchemy.sql import funcret = session.query(Users).group_by(Users.extra).all()ret = session.query(    func.max(Users.id),    func.sum(Users.id),    func.min(Users.id)).group_by(Users.name).all()ret = session.query(    func.max(Users.id),    func.sum(Users.id),    func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()# 连表ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()ret = session.query(Person).join(Favor).all()ret = session.query(Person).join(Favor, isouter=True).all()# 组合q1 = session.query(Users.name).filter(Users.id > 2)q2 = session.query(Favor.caption).filter(Favor.nid < 2)ret = q1.union(q2).all()q1 = session.query(Users.name).filter(Users.id > 2)q2 = session.query(Favor.caption).filter(Favor.nid < 2)ret = q1.union_all(q2).all()

mysql> create database sqldb default character set utf8 collate utf8_general_ci;

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipengine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/sqldb", max_overflow=5)Base = declarative_base()# 一对多关系class User(Base):    __tablename__ = ‘user‘    nid = Column(Integer, primary_key=True,autoincrement=True)    username = Column(String(50))    group_id = Column(Integer, ForeignKey("group.nid"))    # 虚拟关系与Group建立关系，相当于会User生成一个group字段，Group表生成一个uuu字段，实际是不会生成这些字段只是虚拟的关系,其实只是生成了sql语句    group = relationship("Group", backref=‘uuu‘)    def __repr__(self):        """只是打印的时候输出的内容和数据库取数据没有关系"""        temp = "%s:%s:%s" %(self.nid,self.username,self.group_id)        return tempclass Group(Base):    __tablename__ = ‘group‘    nid = Column(Integer, primary_key=True,autoincrement=True)    caption = Column(String(50))def init_db():    Base.metadata.create_all(engine)def drop_db():    Base.metadata.drop_all(engine)init_db()#drop_db()Session = sessionmaker(bind=engine)session = Session()

session.add_all([    Group(caption=‘chuzhong‘),    Group(caption=‘gaozhong‘),    Group(caption=‘daxue‘),])session.add_all([    User(username=‘redhat‘, group_id=1),    User(username=‘centos‘, group_id=2),    User(username=‘fedora‘, group_id=3),    User(username=‘debian‘, group_id=2),    User(username=‘ubuntu‘, group_id=1),    User(username=‘geentoo‘, group_id=3),    User(username=‘archlinux‘, group_id=1),    User(username=‘windows‘, group_id=2),    User(username=‘suse‘, group_id=3),])session.commit()

# select * from user left join group on user.group_id = group.nidsql = session.query(User,Group).join(Group)        # 打印SQL语句print(sql)ret = session.query(User,Group).join(Group).all()  # 默认是内连接print(ret)

sql = session.query(User,Group).join(Group,isouter=True)        # 打印sql语句print(sql)ret = session.query(User,Group).join(Group,isouter=True).all()  # isouter=True 指定外连接,默认是做外连接print(ret)

# 通过传统方式sql = session.query(User.username,Group.caption).join(Group,isouter=True)print(sql)ret = session.query(User.username,Group.caption).join(Group,isouter=True).all()  print(ret)# 通过虚拟关系# 一般relationship 外键设置在哪张表，relationship就设置在哪表，通过这张表查询就叫正向查询，ret = session.query(User).all()for obj in ret:    # obj代指user表的每一行数据    # obj.group代指group对象    print(obj.nid,obj.username,obj.group_id,          obj.group,obj.group.nid,obj.group.caption)

# 传统方式ret = session.query(User.username, Group.caption).join(Group, isouter=True).filter(Group.caption == ‘daxue‘).all()print(ret)# 通过虚拟关系# 反向查询obj = session.query(Group).filter(Group.caption == ‘daxue‘).first()print(obj.nid)print(obj.caption)print(obj.uuu)

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipengine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/sqldb", max_overflow=5)Base = declarative_base()# 多对多关系class Host(Base):    __tablename__ = ‘host‘    nid = Column(Integer, primary_key=True,autoincrement=True)    hostname = Column(String(50))    ip = Column(String(32))    port = Column(String(32))class HostUser(Base):    __tablename__ = ‘host_user‘    nid = Column(Integer, primary_key=True,autoincrement=True)    username = Column(String(32))class HostToHostUser(Base):    __tablename__ = ‘host_to_host_user‘    nid = Column(Integer, primary_key=True,autoincrement=True)  # 保留主键,以后通过找主键删除数据方便    host_id = Column(Integer,ForeignKey(‘host.nid‘))    host_user_id = Column(Integer,ForeignKey(‘host_user.nid‘))    host = relationship(‘Host‘,backref=‘h‘)    host_user = relationship(‘HostUser‘,backref=‘u‘)def init_db():    Base.metadata.create_all(engine)def drop_db():    Base.metadata.drop_all(engine)init_db()# drop_db()Session = sessionmaker(bind=engine)session = Session()

session.add_all([    Host(hostname=‘c1‘,ip=‘1.1.1.1‘,port=‘22‘),    Host(hostname=‘c2‘,ip=‘1.1.1.2‘,port=‘22‘),    Host(hostname=‘c3‘,ip=‘1.1.1.3‘,port=‘22‘),    Host(hostname=‘c4‘,ip=‘1.1.1.4‘,port=‘22‘),    Host(hostname=‘c5‘,ip=‘1.1.1.5‘,port=‘22‘),])session.add_all([    HostUser(username=‘root‘),    HostUser(username=‘redhat‘),    HostUser(username=‘centos‘),    HostUser(username=‘ubuntu‘),])session.add_all([    HostToHostUser(host_id=1,host_user_id=1),    HostToHostUser(host_id=1,host_user_id=2),    HostToHostUser(host_id=1,host_user_id=3),    HostToHostUser(host_id=2,host_user_id=2),    HostToHostUser(host_id=2,host_user_id=4),    HostToHostUser(host_id=2,host_user_id=3),])session.commit()

# 第一步获取Host中用户等于c1的对象host_obj = session.query(Host).filter(Host.hostname == ‘c1‘).first()# host_obj.nid 获取用户等于c1的nid# 第二步通过HostToHostUser表找到HostUser外键对应的host_user_idhost_2_host_user = session.query(HostToHostUser.host_user_id).filter(HostToHostUser.host_id == host_obj.nid).all()print(host_2_host_user)[(1,),(2,),(3,)]r = zip(*host_2_host_user) print(list(r)[0])[1,2,3]# 第三步通过第二步找到HostUser中nid对应的HostUser.usernameusers = session.query(HostUser.username).filter(HostUser.nid.in_(list(r)[0])).all()print(users)可以把上面的步骤全部合并到一起# session.query(Host.nid).filter(Host.hostname == ‘c1‘)# session.query(HostToHostUser.host_user_id).filter(HostToHostUser.host_id == session.query(Host.nid).filter(Host.hostname == ‘c1‘))r = session.query(HostUser.username).filter(HostUser.nid.in_(session.query(HostToHostUser.host_user_id).filter(HostToHostUser.host_id == session.query(Host.nid).filter(Host.hostname == ‘c1‘)))).all()print(r)

# 通过relation虚拟关系中的h字段反向查找，查找到第三表中的对象，然后通过正向查找host_obj = session.query(Host).filter(Host.hostname == ‘c1‘).first()for item in host_obj.h:    print(item.host_user.username)

class HostToHostUser(Base):    __tablename__ = ‘host_to_host_user‘    nid = Column(Integer, primary_key=True,autoincrement=True)  # 保留主键,以后通过找主键删除数据方便    host_id = Column(Integer,ForeignKey(‘host.nid‘))    host_user_id = Column(Integer,ForeignKey(‘host_user.nid‘))# 多对多关系class Host(Base):    __tablename__ = ‘host‘    nid = Column(Integer, primary_key=True,autoincrement=True)    hostname = Column(String(50))    ip = Column(String(32))    port = Column(String(32))    
    # 关系表在User表中,realationship(A,AB.__table,B中的虚拟字段)    host_user = relationship(‘HostUser‘,                             secondary=HostToHostUser.__table__,                             backref=‘h‘)class HostUser(Base):    __tablename__ = ‘host_user‘    nid = Column(Integer, primary_key=True,autoincrement=True)    username = Column(String(32))

host_obj = session.query(Host).filter(Host.hostname == ‘c1‘).first()for item in host_obj.host_user:    print(item.username)