Question

I should extract data from an oracle database.
How can I find out which schema are defined in the database?
When I do not define any schema in the description of Metadata(), I find no tables.
thanks for your help,

Answer 1

Default Oracle schema matches the username that was used in Oracle connection.
If you don’t see any tables – it means the tables are created in another schema.

Looks like you have two questions here:

1) about Oracle schemas – how to find schema and tables in Oracle

2) about SQLAlchemy reflections – how to specify Oracle schema for table

You can find answer for the first question in many places. I.e. here: https://stackoverflow.com/a/2247758/1296661

Answering second question:
Table class constructor has schema argument to specify table’s schema if it is different from default user’s schema. See more here
http://docs.sqlalchemy.org/en/rel_0_7/core/schema.html#sqlalchemy.schema.Table

Here is the python code to answer second question. You will need to setup db connection and table name values to match your case:

from sqlalchemy import Table
from sqlalchemy.ext.declarative import declarative_base


from sqlalchemy import create_engine
engine = create_engine('oracle://<user_name>:<password>@<hostname>:1521/<instance name>', echo=True)
Base = declarative_base()

reflected_table = Table('<Table name>', 
    Base.metadata, 
    autoload=True, 
    autoload_with=engine, 
    schema='<Schema name other then user_name>')
print [c.name for c in reflected_table.columns]

p = engine.execute("SELECT OWNER,count(*) table_count FROM ALL_OBJECTS WHERE OBJECT_TYPE = 'TABLE' GROUP BY OWNER");

for r in p:
    print r

Good luck with using sqlschema and reflection feature – it is a lot of fun. You get your python program working with existing database almost without defining schema information in your program.

I’m using this feature with oracle db in production – the only thing I have to define were relations between tables explicitly setting foreign and primary keys.