2018年5月13日笔记

• SQL语句复习

创建一个库
create database DB_name;
授权一个用户
grant all privileges on *.* to 'user1'@'%' identified by 'qwe123';
创建表
create table table_name(column_name type not null);
查询
select * from tabel_name where condition1 and condition2;
增加
insert into table_name (id, name, age, sex, grander) values (1, 'ling', 25, 'M', 99), (2, 'ajing', 45, 'F', 88);
改
update table_name set column_name=xx where condition
删除
delete from table_name  where condition
drop table table_name
联合查询
select a.id, b.name from A a join B b on a.id=b.tid
创建索引
create index idx_库名_表名_列名1_列名2 (列名1， 列名2)
查看sql是否走索引
explain select * from table_name where column_name=='xxx'

• 连接数据库复习

# python2使用mysqldb
# python3使用pymysql

import pymysql

# 1.创建连接connection和游标cursor
conn = pymysql.connect(host="192.168.2.1", port=3306, user="root", passwd="qwe123", db="test")
cus = conn.cursor()

# 2.执行SQL
sql = "select * from Student;"
cus.execute(sql)
cus.fetchone()
cus.fetchmany(size=n)
cus.fetchall()

# 3.关闭游标cursor和连接connection
cus.close()
conn.close()

• SQLAlchemy复习

# 导入
from sqlalchemy import create_engine, MetaData, Table, Column, Integer, String
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

# 1.创建引擎engine,'数据库类型+数据库驱动名称://用户名:口令@机器地址:端口号/数据库名'
engine = create_engine("mysql+pymysql://username:passwd@hostname:port/db_name")

# 2.创建会话session
DBsession = sessionmaker(bind=engine)
session = DBsession()

# 3.创建表
metadata = MetaData(engine)
student = Table("Student", metadata,
                Column("id", Integer, primary_key=True),
                Column("name", String(50))
                )
metadata.reate_all()       # 若不存在同名Table，则创建

# 4.增加
# 4.1 创建一个模型类
Base =declarative_base()        # 创建对象的基类
class Student(Base):            # 定义一个Student类来表示一张student表，多个表就定义多个class
    __tablename__ = "student"
    id = Column(Integer, primary_key=True)
    name = Column(String(50))
# 4.2 导入模型类，实例化该类
student1 = Student(id=1001, name="Karl")            # ！！！ 别忘了"形参=XXX"  ！！！
student2 = Student(id=1002, name="Tom")
student3 = Student(id=1003, name="Jack")
# 4.3 通过add实例来添加记录
session.add(student1)
session.add_all([student2, student3])

# 5.查询

# 5.1 filter 与 filer_by 的区别

# filter可以使用> <等，表示列必须用 表.列 的形式，等于用 ==.
session.query(Student).filter(Student.id>1000)
# filter不支持组合查询
session.query(Student).filter(Student.id>1000).filter(name=="Tom")

# filter_by可直接写列，不支持> <，等于用 ==
# filter_by可支持组合查询
session.query(Student).filter(id==1000 and name=="Jack")

# 5.2 模糊查询
# SQL语句的模糊查询
#select * from student where name like '%ling%';
# python语句的模糊查询
session.query(Student).filter(Student.name.like("%ling%"))

# 5.3 获取数据
one()   tuple
all()   list
# 在查询中，不写one()或all()，获取的结果就是SQL语句

# 6.更新
# 6.1 先查出来
std1 = session.query(Student).filter(Student.id>1000)
# 6.2 更新类的属性值
std1.name = "testname"
# 6.3 commit提交下
session.commit()

# 7.删除
# 先查出来，然后调用delete()方法，左后commit()
session.delete(std1)

# 8.统计、分组、排序
# 8.1 统计
session.query().filter().count()
session.query().filter().groupby()
session.query().filter().orderby(student.id.desc)

• 将对数据库的操作进行封装

from sqlalchemy import create_engine, Integer, String, Column
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base



Base = declarative_base()
class Student(Base):
    __tablename__ = 'student'
    id = Column(Integer, primary_key=True)
    name = Column(String(50))
    age = Column(Integer)
    address = Column(String(100))

# 增
def insert(session):
    student1 = Student(id=1004, name='ling', age=28, address='shanxi')
    session.add(student1)
    session.commit()

# 删
def delete(session):
    session.query(Student).filter(Student.id == 1001).delete()
    session.commit()

# 改
def update(session):
    student1 = session.query(Student).filter(Student.id == 1001).one()
    student1.name = 'test123'
    session.commit()
    student2 = session.query(Student).filter(Student.id == 1001).one()
    print(student2.name)

# 统计
def count(session):
    numnber = session.query(Student).filter().count()
    print("total student is {0}".format(numnber))

# 分组
def groupBy(session):
    groupByAge = session.query(Student).group_by(Student.age).all()
    print(groupByAge)
    for i in groupByAge:
        print(i.id, i.name, i.age, i.address)

# 排序
def orderBy(session):
    orderByAge = session.query(Student).order_by(Student.age.desc()).all()
    for x in orderByAge:
        print(x.id, x.name, x.age, x.address)



def main():
    engine = create_engine('mysql+pymysql://xiang:xiang@192.168.48.136/sqlalchemy')
    DBsession = sessionmaker(bind=engine)
    session = DBsession()
    # insert(session)
    # update(session)
    # delete(session)
    # count(session)
    # groupBy(session)
    orderBy(session)


if __name__ == '__main__':
    main()