Python:sqlalchemy連線資料庫
阿新 • • 發佈:2018-12-27
安裝:
pip install sqlalchemy
# 安裝資料庫驅動:
pip install pymysql
pip install cx_oracle
舉例:(在url後面加入?charset=utf8可以防止亂碼)
from sqlalchemy import create_engine
engine=create_engine('mysql+pymysql://username:[email protected]:port/dbname', echo=True) #echo=True 列印sql語句資訊
create_engine
接受一個url,格式為:
# '資料庫型別+資料庫驅動名稱://使用者名稱:口令@機器地址:埠號/資料庫名'
# 常用的
engine = create_engine('sqlite:///:memory:', echo=True) # sqlite記憶體
engine = create_engine('sqlite:///./cnblogblog.db',echo=True) # sqlite檔案
engine = create_engine("mysql+pymysql://username:[email protected]:port/dbname",echo=True) # mysql+pymysql
engine = create_engine('mssql+pymssql://username:[email protected]:port/dbname',echo=True) # mssql+pymssql
engine = create_engine('postgresql://scott:[email protected]:5432/dbname') # postgresql示例
engine = create_engine('oracle://scott:[email protected]:1521/sidname') # oracle
engine = create_engine('oracle+cx_oracle://scott: [email protected]') #pdb就可以用tns連線
簡單demo:
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
engine = create_engine('oracle://spark:[email protected]',echo=True) #echo要求列印sql語句等除錯資訊
session_maker = sessionmaker(bind=engine)
session = session_maker()
Base = declarative_base()
#對應一張表
class Student(Base):
__tablename__ = 'STUDENT'
id = Column('STUID', Integer, primary_key=True)
name = Column('STUNAME', String(32), nullable=False)
age = Column('STUAGE', Integer)
def __repr__(self):
return '<Student(id:%s, name:%s, age:%s)>' % (self.id, self.name, self.age)
Base.metadata.create_all(engine) #若存在STUDENT表則不做,不存在則建立。
queryObject = session.query(Student).order_by(Student.id.desc())
for ins in queryObject:
print(ins.id, ins.name, ins.age)
'''
4 hey 24
3 lwtxxs 27
2 gyb 89
1 ns 23
'''
將查詢結果對映為DataFrame:
import pandas as pd
df = pd.read_sql(session.query(Student).filter(Student.id > 1).statement, engine)
print(df)
'''
STUID STUNAME STUAGE
0 4 hey 24
1 2 gyb 89
2 3 lwtxxs 27
'''
查詢:
session的query方法除了可以接受Base子類物件作為引數外,還可以是欄位,如:
query = session.query(Student.name, Student.age) # query為一個sqlalchemy.orm.query.Query物件
for stu_name, stu_age in query:
print(stu_name, stu_age)
查詢條件filter:
# = / like
query.filter(Student.name == 'wendy')
query.filter(Student.name.like('%ed%'))
# in
query.filter(Student.name.in_(['wendy', 'jack']))
query.filter(Student.name.in_(
session.query(User.name).filter(User.name.like('%ed%'))
))
# not in
query.filter(~Student.name.in_(['ed', 'wendy', 'jack']))
# is null / is not null
query.filter(Student.name == None)
query.filter(Student.name.is_(None))
query.filter(Student.name != None)
query.filter(Student.name.isnot(None))
# and
from sqlalchemy import and_, or_
query.filter(and_(Student.name == 'ed', Student.age != 23))
query.filter(Student.name == 'ed', Student.age != 23)
query.filter(Student.name == 'ed').filter(Student.age != 23)
# or
query.filter(or_(Student.name == 'ed', Student.name == 'wendy'))
# match
query.filter(Student.name.match('wendy'))
Query的方法:
all()
方法以列表形式返回結果集:
from sqlalchemy import or_, and_
queryObject = session.query(Student).filter(or_(Student.id == 1, Student.id == 2))
print(queryObject.all()) # [<Student(id:1, name:ns, age:23)>, <Student(id:2, name:gyb, age:89)>]
queryObject = session.query(Student.name).filter(or_(Student.id == 1, Student.id == 2))
print(queryObject.all()) # [('ns',), ('gyb',)]
first()
方法返回單個結果。(若結果集為空則返回None
)
print(queryObject.first()) # ('ns',)
one()
方法返回單個結果,與first()
方法不同的是:當結果集中沒有元素或有多於一個元素會丟擲異常。
one_or_none()
方法同one()
一樣,不同是結果集為空則返回None
,為多個丟擲異常。
查詢數量:
from sqlalchemy import func
session.query(func.count(Student.id)).scalar() # SELECT count("STUDENT"."STUID") AS count_1 FROM "STUDENT"
分組:
session.query(func.count(Student.id), Student.name).group_by(Student.name).all()
巢狀SQL語句:
from sqlalchemy import text
query = session.query(Student.id, Student.name).filter(text('stuid>2'))
query = session.query('stuid', 'stuname', 'stuage').from_statement(\
text("select * from student where stuname=:stuname")).params(stuname='hey').all() #[(4, 'hey', 24)]