简单查询

print(session.query(User).all())
print(session.query(User.name, User.fullname).all())
print(session.query(User, User.name).all())

带条件查询

print(session.query(User).filter_by(name='user1').all())
print(session.query(User).filter(User.name == "user").all())
print(session.query(User).filter(User.name.like("user%")).all())

多条件查询

print(session.query(User).filter(and_(User.name.like("user%"), User.fullname.like("first%"))).all())
print(session.query(User).filter(or_(User.name.like("user%"), User.password != None)).all())

sql过滤

print(session.query(User).filter("id>:id").params(id=1).all())

关联查询

print(session.query(User, Address).filter(User.id == Address.user_id).all())
print(session.query(User).join(User.addresses).all())
print(session.query(User).outerjoin(User.addresses).all())

聚合查询

print(session.query(User.name, func.count('*').label("user_count")).group_by(User.name).all())
print(session.query(User.name, func.sum(User.id).label("user_id_sum")).group_by(User.name).all())

子查询

stmt = session.query(Address.user_id, func.count('*').label("address_count")).group_by(Address.user_id).subquery()
print(session.query(User, stmt.c.address_count).outerjoin((stmt, User.id == stmt.c.user_id)).order_by(User.id).all())

exists

print(session.query(User).filter(exists().where(Address.user_id == User.id)))
print(session.query(User).filter(User.addresses.any()))
--deals=交易表,areas=地域表,例如香港;我们的目的:查看有交易的地域

select * from areas where id in (select city_id from deals);

select * from areas where id in (select city_id from deals where deals.city_id = areas.id);

select * from areas where exists (select null from deals where deals.city_id = areas.id);

区别:
EXISTS语法并没有说哪个字段落在了子查寻的结果中,而是说exists后面的语句执行的结果是不是有记录,只要有记录,则主查询语句就成立。它代表‘存在’,用来引领嵌套查询的子查询,它不返回任何数据,只产生逻辑真值‘true’与逻辑假值‘False’。由EXISTS引出的子查询,其目标列表达式通常都用*(用null也可以),因为带有EXISTS的子查询只返回真值或假值,给出列名没有实际意义

限制返回字段查询

person = session.query(Person.name, Person.created_at,
Person.updated_at).filter_by(name=”zhongwei”).order_by(
Person.created_at).first()

记录总数查询:

from sqlalchemy import func

count User records, without

using a subquery.

session.query(func.count(User.id))

return count of user “id” grouped

by “name”

session.query(func.count(User.id)).\
group_by(User.name)

from sqlalchemy import distinct

count distinct “name” values

session.query(func.count(distinct(User.name)))