# 63 limit、offset以及切片操作 1. limit:可以限制每次查詢的時候只查詢幾條數據。 1. ```text 獲取前10條數據 articles = session.query(Article).limit(10).all() ``` 2. offset:可以限制查找數據的時候過來前面多少條。 1. ```text # select * from article limit 4 offset 9 # select * from article limit 9,4 # articles = session.query(Article).order_by(Article.id.desc()).offset(10).limit(10).all() # slice(limit,offset),desc()降序 # articles = session.query(Article).order_by(Article.id.desc()).slice(0,10).all() ``` 3. 切片:可以Query對象使用切片操作，來獲取想要的數據 1. ```text articles = session.query(Article).order_by(Article.id.desc())[0:10] ``` ```text from sqlalchemy.ext.declarative import declarative_base from sqlalchemy import create_engine, String, Integer, Float, ForeignKey, DateTime, Date, Column, desc,asc from sqlalchemy.dialects.mysql import LONGTEXT from sqlalchemy.orm import sessionmaker,relationship,backref from datetime import datetime HOSTNAME = "127.0.0.1" PORT = "3306" USERNAME = "root" PASSWORD = "123456" DATABASE = "xt_flask" DB_URI = "mysql+pymysql://{}:{}@{}:{}/{}?charset=utf8".format(USERNAME,PASSWORD,HOSTNAME,PORT,DATABASE) engine = create_engine(DB_URI) Base = declarative_base(engine) session = sessionmaker(engine)() class Article(Base): __tablename__ = "article" id = Column(Integer,primary_key=True,autoincrement=True) title = Column(String(50),nullable=False) create_time = Column(DateTime,default=datetime.now) def __repr__(self): return "<Article(title:%s,create_time:%s)>" % (self.title,self.create_time) # 添加數據 # Base.metadata.drop_all() # Base.metadata.create_all() # # for i in range(100): # title = "title %s" % i # article = Article(title=title) # session.add(article) # session.commit() # 實戰 # articles = session.query(Article).all() # 獲取前10條數據 # articles = session.query(Article).limit(10).all() # offset(10)代表從第幾條的數據開始 # select * from article limit 4 offset 9 # select * from article limit 9,4 # articles = session.query(Article).order_by(Article.id.desc()).offset(10).limit(10).all() # slice(limit,offset),desc()降序 # articles = session.query(Article).order_by(Article.id.desc()).slice(0,10).all() # 切片 articles = session.query(Article).order_by(Article.id.desc())[0:10] print(articles) ```