以下所有代码片段都使用了统一的引用，该引用如下：

from sqlalchemy import create_engine, ForeignKey

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, String, Integer, Table

from sqlalchemy.orm import relationship, sessionmaker

engine = create_engine("mysql+pymysql://root:root@localhost/study?charset=utf8", echo=True)  # 连接数据库,显示SQL语句

Base = declarative_base()  # 创建基类

class Student(Base):

    __tablename__ = 'students'  # 指定表名

    __table_args__ = {

        # "mysql_engine":"MyISAM",

        "mysql_charset":"utf8"

    }

    # show create table students 可以查看建表语句;默认是Innodb,lating-1.如果想显示中文需要修改指定建表的类型,同时,engine也要指定编码格式

    id = Column(Integer, primary_key=True)

    name = Column(String(30))

    gender = Column(Integer)

    std_id = Column(String(10))

    teacher = Column(String(30))

    def __str__(self):

        return self.name

Base.metadata.create_all(engine)  # 创建所有继承自 Base 的类对应的表

sqlslchemy在数据库中创建表之前，会先检查该表是否存在，如果不存在，才会去创建新表

class Student(Base):

    __tablename__ = 'students'  # 指定表名

    id = Column(Integer, primary_key=True)

    name = Column(String(30))

    gender = Column(Integer)

    std_id = Column(String(10))

    teacher = Column(String(30))

    **math = Column(Integer)**

    def __str__(self):

        return self.name

虽然新加了一个math 变量（字段），但是由于数据库中已有students表，所以不会去创建新表，match字段也就不存在

插入数据

Session = sessionmaker(bind=engine)  # 获取 Session类

ses = Session()  # 获取session对象

zhangsan = Student(name="zhangsan", gender=1, std_id='XS331', teacher='hanmeimei', math=90)

lisi = Student(name="lisi", gender=1, std_id='XS332', teacher='hanmeimei', math=10)

wangwu = Student(name="wangwu", gender=0, std_id='XS333', teacher='lilei', math=60)

zhaoliu = Student(name="zhaoliu", gender=0, std_id='XS337', teacher='lilei', math=80)

ses.add(zhangsan)  # 单条添加

ses.add_all([lisi, wangwu, zhaoliu])  # 批量添加

ses.commit()

修改数据

zhangsan = ses.query(Student).filter_by(name='zhangsan').first()

zhangsan.math = 91

ses.commit()

也可以在还创建数据的时候，修改

liqi = Student(name="liqi", gender=1, std_id='XS335', teacher='xiadonghai', math=100)

ses.add(liqi)

liqi = ses.query(Student).filter_by(name='liqi').first()

liqi.gender = 0

ses.commit()

liqi = Student(name="liqi", gender=1, std_id='XS335', teacher='xiadonghai', math=100)

liqi.gender = 0

ses.add(liqi)

ses.commit()

sess.query(Student).filter_by(name='liming').update({'gender':0})

sess.commit()

删除

# result = sess.query(Student).filter(Student.id == 1 ).delete()

# sess.commit()

# result = sess.query(Student).filter(Student.id == 2 ).first()

# sess.delete(result)

# sess.commit()

查询

# = 操作符

# students_99 = sess.query(Student).filter_by(name ='zhangsan').all()

# students_100 = sess.query(Student).filter(Student.name == 'zhangsan').all()

# for i in students_100:

#    print(i.name)

# ！= 操作符

# student_101 = sess.query(Student).filter_by(name != 'liming').all()  # error

# student_98 = sess.query(Student).filter(Student.name != 'liming').all()

# for i in student_98:

#   print(i.name)

#  > ,<, <=, >=, 操作符

# student_60 = sess.query(Student).filter(Student.math > 10).all()

# student_61= sess.query(Student).filter_by(math>10).all()  # error

# student_62 = sess.query(Student).filter(Student.math < 100).all()

# student_63 = sess.query(Student).filter(Student.math <= 90).all()

# student_64 = sess.query(Student).filter(Student.math >= 90).all()

# student_64 = sess.query(Student).filter(Student.math <> 90).all()  # error

# for i in student_60:

#     print(i.math)

# for i in student_62:

#     print(i.math)

# for i in student_63:

#     print(i.math)

# for i in student_64:

#     print(i.math)

# 根据主键获取对象

# students_1 = sess.query(Student).get(1)

# print(students_1

# value指定要获取的字段 返回的是生成器

# students_3  = sess.query(Student).value(Student.name)

# print(students_3)

# values 指定多个字段 返回的是生成器

# students_3_2  = sess.query(Student).values(Student.id,Student.name)

# print(students_3_2)

# for i in students_3_2:

#     print(i)

# 一次获取多个字段值

# students_4 = sess.query(Student.name,Student.gender).all()

# print(students_4)

# for i in students_4:

#     print(i)

# 后续添加的方式选择要得到的字段结果

# students_5 = sess.query(Student.name).add_columns(Student.gender).all()

# print(students_5)

# student_6 = sess.query(Student).filter_by(name="王大麻子").one()

# print(student_6)

# 字段别名

# student_7 = sess.query(Student.name.label('std_name')).all()

# print(student_7)

# for i in student_7:

#     print(i.std_name)

#     print(i[0])  # 第二种取值方式

# student_8 = sess.query(Student.name).all()

# print(student_8)

# for i in student_8:

#     print(i.name)

#     print(i[0])

# 分页

# student_10 = sess.query(Student).limit(2).offset(1).all()

# student_11 = sess.query(Student).offset(1).limit(2).all()

# student_12 = sess.query(Student)[1:3]

# for i in student_10:

#     print(i.id)

# for i in student_11:

#     print(i.id)

# for i in student_12:

#     print(i.id)

# filter 和 filter_by

# student_13 = sess.query(Student).filter_by(id=1).one_or_none()

# student_14 = sess.query(Student).filter(Student.id == 1).one_or_none()

# print(student_13)

# print(student_14)

# chain 链式调用

# student_15 = sess.query(Student).filter_by(gender=1).filter(Student.math>80).all()

# # student_15_2 = sess.query(Student).filter_by(gender=1).filter_by(math>80).all()  # error

# student_16 = sess.query(Student).filter(Student.gender == 1).filter(Student.math>80).all()

# for i in student_15:

#     print(i.name)

# for i in student_16:

#     print(i.name)

# like 操作符  % 代表任意多个字符  _ 代表一个字符

# student_17 = sess.query(Student).filter(Student.name.like("%i%")).all()

# for i in student_17:

#     print(i.name)

# student_17_2 = sess.query(Student).filter(Student.name.like("%i_i")).all()

# for i in student_17_2:

#     print(i.name)

# not like

# student_70 = sess.query(Student).filter(~Student.name.like("%i_i")).all()

# student_71 = sess.query(Student).filter(Student.name.notlike("%i_i")).all()

# for i in student_70:

#     print(i.name)

# print(student_70 == student_71)

# in 操作符

# student_18 = sess.query(Student).filter(Student.name.in_(['zhangsan','lisi','wangwu'])).all()

# for i in student_18:

#     print(i.name)

# not in

# student_19 = sess.query(Student).filter(~Student.name.in_(['lisi'])).all()

# student_19_2 = sess.query(Student).filter(Student.name.notin_(['lisi'])).all()

# for i in student_19:

#     print(i.name)

# print(student_19 == student_19_2)

# 是否为null

# student_20 = sess.query(Student).filter(Student.name != None).all()

# student_21 = sess.query(Student).filter(~Student.name.is_(None)).all()

# student_22 = sess.query(Student).filter(Student.name.isnot(None)).all()

# student_21_3 = sess.query(Student).filter(Student.name.is_('zhangsan')).all()  # error

# student_21_2 = sess.query(Student).filter(Student.name.is_(1)).all()

# for i in student_20:

#     print(i.name)

# print(student_20 == student_21 == student_22)

# student_23 = sess.query(Student).filter(Student.math.is_(90)).all()

# student_24 = sess.query(Student).filter(Student.math == None).all()

# 类别名

# flower = aliased(Student)

# student_9 = sess.query(flower.name).all()

# print(student_9)

# and

# student_25 = sess.query(Student).filter(Student.gender == 1, Student.math > 70).all()

# student_26 = sess.query(Student).filter(and_(Student.gender == 1, Student.math > 70)).all()  # 别忘了引入该方法

# student_27 = sess.query(Student).filter(Student.gender == 1).filter(Student.math > 70).all()

# for i in student_25:

#     print(i.name)

# print(student_25 == student_26 == student_27)

# or

# student_28 = sess.query(Student).filter(or_(Student.gender == 1, Student.math > 80)).all()

# for i in student_28:

#     print(i.name)

# 错误用法

# error_1 = sess.query(Student).filter_by(and_(Student.id == 1, Student.name == 'lisi')).first()

# error_2 = sess.query(Student).filter_by(and_(id=1, name='lisi')).first()

# error_3 = sess.query(Student).filter(and_(id=1, name='lisi')).first()

# one 有且只有一个，否则报错

# student_30 = sess.query(Student).filter(Student.id == 1).one()

# print(student_30)

# 可以只有一个或者没有，不能为多个结果，否则报错

# student_31 = sess.query(Student).filter(Student.id == 10).one_or_none()

# print(student_31)

# text  原生sql条件语句

# student_31 = sess.query(Student).filter(text("name='lisi'")).first()  # 注意值为字符串时的写法

# student_32 = sess.query(Student).filter(text("id=1")).first()  # 注意值为 数字 的写法

# student_31 = sess.query(Student).filter(text("id>1 and math>10")).all()

# for i in student_31:

#     print(i.name)

# order_by 排序

# student_33 = sess.query(Student).filter(text("math >= 10")).order_by(~text("math")).all()  # 逆序

# student_33_2 = sess.query(Student).filter(text("math >= 10")).order_by(text("math")).all()  # 顺序

# student_33_2_1 = sess.query(Student).filter(text("math >= 10")).order_by(desc(text("math"))).all()  # 逆序

# student_33_3 = sess.query(Student).order_by(desc(Student.math)).all()  # 逆序

# student_33_4 = sess.query(Student).order_by(Student.math.desc()).all()  # 逆序

# student_33_5 = sess.query(Student).order_by(~Student.math).all()  # 逆序

# student_33_6 = sess.query(Student).order_by(Student.math).all()  # 顺序

# print(student_31)

# print(student_32)

# print("___"* 30)

# for i in student_33:

#     print(i.math)

# print("___"* 30)

# for i in student_33_2:

#     print(i.math)

# for i in student_33_3:

#     print(i.math)

# for i in student_33_4:

#     print(i.math)

# for i in student_33_5:

#     print(i.math)

# for i in student_33_6:

#     print(i.math)

# text 插入变量

# student_34 =sess.query(Student).filter(text("gender=:sex and math>:score")).params(sex=1, score=1).all()

# for i in student_34:

#     print(i.name)

# from_statement 原生sql语句

# student_35 = sess.query(Student).from_statement(text("select * from students where id=:id")).params(id=1).one()

# student_36 = sess.query(Student).from_statement("select * from students where math>:score").params(score=10).all()

# student_36_1 = sess.query(Student).from_statement("select * from students where math>10").all()

# print(student_35)

# for i in student_36:

#     print(i.name)

# print(student_36 == student_36_1)

# count

# student_38 = sess.query(Student).filter_by(gender=1).count()

# student_38_2 = sess.query(func.count(Student.name),Student.name).group_by(Student.name).all()

# student_38_3 = sess.query(func.count(Student.name),Student.gender).group_by(Student.gender).all()

# print(student_38_2)

# print(student_38_3)

# group_by 分组

# student_39 = sess.query(Student).group_by(Student.gender == 1).count()

# print(student_39)

# having

# student_39_1 = sess.query(Student).group_by(Student.gender == 1).having(Student.math>60).all()

# for i in student_39_1:

#     print(i)

# distinct

# student_40 = sess.query(distinct(Student.name)).all()

# for i in student_40:

#     print(i)

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