索引 ?
主键?
分页:
limit marker offset sort
if page_size:
query = query.limit(page_size)
if page:
query = query.offset(page*page_size)
排序:
order_by
DBError: (psycopg2.ProgrammingError) column reference "ID" is ambiguous
解决办法:
query = query(context, models.InstanceGroup).order_by("id")
↓↓↓
query = query(context, models.InstanceGroup).order_by(models.InstanceGroup.id)
select_from查询的理解
q = session.query(Address).select_from(User).join(User.addresses).filter(User.name == 'ed')
SELECT address.* FROM user JOIN address ON user.id=address.user_id WHERE user.name = :name_1
sql连接语句中on和where区别:
1)left join
(SQL> select * from A left join B on A.id = B.id and A.type = xx;)
1. on条件是在生成临时表时使用的条件,它不管on中的条件是否为真,都会返回左边表中的记录。
2. where条件是在临时表生成好后,再对临时表进行过滤的条件,条件不为真的就全部过滤掉。
(on后的条件用来生成左右表关联的临时表,where后的条件对临时表中的记录进行过滤。)
(如果and语句是对左表进行过滤的,那么不管真假都不起任何作用。如是对右表过滤的,那么左表所有记录都返回,右表筛选后再与左表连接返回)
2)inner join
(SQL> select * from A inner join B on A.id = B.id and A.type = xx;)
1. 不管是对左表还是右表进行筛选,on and和on where都会对生成的临时表进行过滤。
python交互数据库操作
import sys from sqlalchemy import create_engine from sqlalchemy.orm import sessionmaker import json import os from oslo_config import cfg from sqlalchemy.orm import joinedload import re CONF = cfg.CONF from FSSecurity.crypt import encrypt from nova.nova_extension.db.sqlalchemy import models as ext_models from nova.db.sqlalchemy import models as models database_connect = cfg.StrOpt('connection', help='database connection',secret=True) CONF(args='', default_config_files=['/etc/nova/nova-conductor.conf']) CONF.register_opt(database_connect, group='database') engine = create_engine(CONF.database.connection, echo=True) db_session = sessionmaker(bind=engine) session = db_session(autocommit=True) session.query(models.QuotaUsage).filter_by(id =16).update({'in_use':20})