读取一范围数据 - LIMIT 和 OFFSET¶
现在你已经知道如何使用 .one()、.first() 和 session.get() 获取单行数据。
你也知道如何使用 .where() 进行筛选来获取多行数据。
接下来，让我们看看如何只获取一个 结果范围。
创建数据¶
我们将继续使用之前的代码，但会稍微修改 select_heroes() 函数，以简化示例并专注于我们想要实现的目标。
再次，我们将创建几个英雄，以便有一些数据可以选择：
# Code above omitted 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
# Code below omitted 👇
# Code above omitted 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: int | None = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: Optional[int] = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
回顾选择所有数据¶
这是我们在 select() 示例中选择所有英雄的代码：
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
但这将一次性获取 所有 英雄，假设数据库中可能有成千上万的数据，这样做可能会造成问题。
使用 Limit 选择¶
目前，我们的数据库中有 7 个英雄。但是我们也可能有成千上万的英雄，因此我们可以使用 limit 限制结果，只获取前 3 个：
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: int | None = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: Optional[int] = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
我们从 select() 获得的特殊 select 对象也有一个 .limit() 方法，我们可以使用它来限制结果的数量。
在这个例子中，我们不再获取所有的 7 行数据，而是将其限制为只获取前 3 行。
在命令行运行程序¶
如果我们在命令行中运行程序，它会输出如下：
太好了！我们得到了 3 个英雄，正如我们所希望的那样。
Tip
稍后我们将更详细地查看 SQL 代码。
使用 Offset 和 Limit 进行选择¶
现在我们可以限制结果，获取前 3 个英雄。
但是假设我们正在一个用户界面中显示结果，每次显示 3 个英雄。
Tip
这种方式通常被称为“分页”。因为用户界面通常会一次显示一“页”预定义数量的英雄。
然后，你可以与界面交互来获取下一页，以此类推。
如何获取接下来的 3 个英雄呢？
我们可以使用 .offset() 方法：
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(3).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(3).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: int | None = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(3).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: Optional[int] = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(3).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
这种方法的工作原理是，我们从 select() 得到的特殊 select 对象有一些方法，例如 .where()、.offset() 和 .limit()。
每个方法都会在内部的特殊选择语句对象上应用变更，并且 返回相同的对象 ，这样我们就可以继续在其上使用更多方法，就像上面的例子中，我们同时使用了 .offset() 和 .limit()。
Offset 意味着“跳过这么多行”，而我们要跳过已经查看过的前三行，因此我们使用 .offset(3)。
在命令行中使用 Offset 运行程序¶
现在我们可以在命令行中运行程序，它会输出如下：
选择下一批数据¶
然后，为了获取下一批 3 行数据，我们需要跳过前面已经看到的 6 行：
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(6).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(6).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: int | None = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(6).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: Optional[int] = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).offset(6).limit(3)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
目前数据库中只有 7 行，所以这个查询只能获取 1 行数据。
但不用担心，数据库不会因为只剩 1 行数据就抛出错误（就像在 Python 列表中会发生的情况）。
数据库知道我们想要 限制 结果的数量，但它不一定需要找到那么多结果。
在命令行中运行最后一批数据¶
如果我们在命令行中运行程序，它会输出如下：
SQL 中的 LIMIT 和 OFFSET¶
你可能注意到 SQL 中的新关键字 LIMIT 和 OFFSET。
你可以在 SQL 中使用它们，位于其他部分的后面：
SELECT id, name, secret_name, age
FROM hero
LIMIT 3 OFFSET 6
如果你在 DB Browser for SQLite 中尝试这个 SQL 查询，你会得到相同的结果：
将 Limit 和 Offset 与 Where 结合使用¶
当然，你也可以将 .limit() 和 .offset() 与 .where() 以及你稍后将学到的其他方法结合使用：
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.age > 32).offset(1).limit(2)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
# Code above omitted 👆
def select_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.age > 32).offset(1).limit(2)
results = session.exec(statement)
heroes = results.all()
print(heroes)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: int | None = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.age > 32).offset(1).limit(2)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine, select
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str = Field(index=True)
secret_name: str
age: Optional[int] = Field(default=None, index=True)
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"
engine = create_engine(sqlite_url, echo=True)
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
hero_4 = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
hero_5 = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
hero_6 = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
hero_7 = Hero(name="Captain North America", secret_name="Esteban Rogelios", age=93)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
session.add(hero_4)
session.add(hero_5)
session.add(hero_6)
session.add(hero_7)
session.commit()
def select_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.age > 32).offset(1).limit(2)
results = session.exec(statement)
heroes = results.all()
print(heroes)
def main():
create_db_and_tables()
create_heroes()
select_heroes()
if __name__ == "__main__":
main()
在命令行中运行包含 Limit、Offset 和 Where 的程序¶
如果我们在命令行中运行程序，它将查找数据库中所有年龄大于 32 的英雄。通常这会是 4 个英雄。
但是我们从偏移量为 1 的位置开始（因此不计算第一个），并将结果限制为仅获取后面两个英雄：
总结¶
无论你如何使用 .where() 或其他方法筛选数据，你都可以使用 .limit() 来限制查询结果的最大数量。
同样，你可以使用 .offset() 跳过前面的结果。