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

 1 # python2使用mysqldb
 2 # python3使用pymysql
 3
 4 import pymysql
 5
 6 # 1.创建连接connection和游标cursor
 7 conn = pymysql.connect(host="192.168.2.1", port=3306, user="root", passwd="qwe123", db="test")
 8 cus = conn.cursor()
 9
10 # 2.执行SQL
11 sql = "select * from Student;"
12 cus.execute(sql)
13 cus.fetchone()
14 cus.fetchmany(size=n)
15 cus.fetchall()
16
17 # 3.关闭游标cursor和连接connection
18 cus.close()
19 conn.close()

• SQLAlchemy复习

 1 # 导入
 2 from sqlalchemy import create_engine, MetaData, Table, Column, Integer, String
 3 from sqlalchemy.orm import sessionmaker
 4 from sqlalchemy.ext.declarative import declarative_base
 5
 6 # 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‘
 7 engine = create_engine("mysql+pymysql://username:[email protected]:port/db_name")
 8
 9 # 2.创建会话session
10 DBsession = sessionmaker(bind=engine)
11 session = DBsession()
12
13 # 3.创建表
14 metadata = MetaData(engine)
15 student = Table("Student", metadata,
16                 Column("id", Integer, primary_key=True),
17                 Column("name", String(50))
18                 )
19 metadata.reate_all()       # 若不存在同名Table，则创建
20
21 # 4.增加
22 # 4.1 创建一个模型类
23 Base =declarative_base()        # 创建对象的基类
24 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
25     __tablename__ = "student"
26     id = Column(Integer, primary_key=True)
27     name = Column(String(50))
28 # 4.2 导入模型类，实例化该类
29 student1 = Student(id=1001, name="Karl")            # ！！！ 别忘了"形参=XXX"  ！！！
30 student2 = Student(id=1002, name="Tom")
31 student3 = Student(id=1003, name="Jack")
32 # 4.3 通过add实例来添加记录
33 session.add(student1)
34 session.add_all([student2, student3])
35
36 # 5.查询
37
38 # 5.1 filter 与 filer_by 的区别
39
40 # filter可以使用> <等，表示列必须用 表.列 的形式，等于用 ==.
41 session.query(Student).filter(Student.id>1000)
42 # filter不支持组合查询
43 session.query(Student).filter(Student.id>1000).filter(name=="Tom")
44
45 # filter_by可直接写列，不支持> <，等于用 ==
46 # filter_by可支持组合查询
47 session.query(Student).filter(id==1000 and name=="Jack")
48
49 # 5.2 模糊查询
50 # SQL语句的模糊查询
51 #select * from student where name like ‘%ling%‘;
52 # python语句的模糊查询
53 session.query(Student).filter(Student.name.like("%ling%"))
54
55 # 5.3 获取数据
56 one()   tuple
57 all()   list
58 # 在查询中，不写one()或all()，获取的结果就是SQL语句
59
60 # 6.更新
61 # 6.1 先查出来
62 std1 = session.query(Student).filter(Student.id>1000)
63 # 6.2 更新类的属性值
64 std1.name = "testname"
65 # 6.3 commit提交下
66 session.commit()
67
68 # 7.删除
69 # 先查出来，然后调用delete()方法，左后commit()
70 session.delete(std1)
71
72 # 8.统计、分组、排序
73 # 8.1 统计
74 session.query().filter().count()
75 session.query().filter().groupby()
76 session.query().filter().orderby(student.id.desc)

• 将对数据库的操作进行封装

 1 from sqlalchemy import create_engine, Integer, String, Column
 2 from sqlalchemy.orm import sessionmaker
 3 from sqlalchemy.ext.declarative import declarative_base
 4
 5
 6
 7 Base = declarative_base()
 8 class Student(Base):
 9     __tablename__ = ‘student‘
10     id = Column(Integer, primary_key=True)
11     name = Column(String(50))
12     age = Column(Integer)
13     address = Column(String(100))
14
15 # 增
16 def insert(session):
17     student1 = Student(id=1004, name=‘ling‘, age=28, address=‘shanxi‘)
18     session.add(student1)
19     session.commit()
20
21 # 删
22 def delete(session):
23     session.query(Student).filter(Student.id == 1001).delete()
24     session.commit()
25
26 # 改
27 def update(session):
28     student1 = session.query(Student).filter(Student.id == 1001).one()
29     student1.name = ‘test123‘
30     session.commit()
31     student2 = session.query(Student).filter(Student.id == 1001).one()
32     print(student2.name)
33
34 # 统计
35 def count(session):
36     numnber = session.query(Student).filter().count()
37     print("total student is {0}".format(numnber))
38
39 # 分组
40 def groupBy(session):
41     groupByAge = session.query(Student).group_by(Student.age).all()
42     print(groupByAge)
43     for i in groupByAge:
44         print(i.id, i.name, i.age, i.address)
45
46 # 排序
47 def orderBy(session):
48     orderByAge = session.query(Student).order_by(Student.age.desc()).all()
49     for x in orderByAge:
50         print(x.id, x.name, x.age, x.address)
51
52
53
54 def main():
55     engine = create_engine(‘mysql+pymysql://xiang:[email protected]/sqlalchemy‘)
56     DBsession = sessionmaker(bind=engine)
57     session = DBsession()
58     # insert(session)
59     # update(session)
60     # delete(session)
61     # count(session)
62     # groupBy(session)
63     orderBy(session)
64
65
66 if __name__ == ‘__main__‘:
67     main()

原文地址：https://www.cnblogs.com/karl-python/p/9038700.html