SQLAlchemy Dialect for EXASOL DB
This is an SQLAlchemy dialect for the EXASOL database.
How to get started
We assume you have a good understanding of (unix)ODBC. If not, make sure you read their documentation carefully - there are lot's of traps to step into.
Get the EXASolution database
If you do not have access to an EXASolution database, download EXASolo for free from EXASOL: http://www.exasol.com/en/test-drive/
The database is a VM image. You will need VirtualBox, VMWare Player, or KVM to run the database. Start the database and make sure you can connect to it as described in the How-To from EXASOL.
Meet the system requirements
On Linux/Unix like systems you need:
- the packages unixODBC and unixODBC-dev >= 2.2.14
- Python >= 2.7
- Download and install the ODBC client drivers from EXASOL >= 5
- configure ODBC.ini and ODBCINST.ini
- Turbodbc and sqlalchemy_exasol as well do now support python 2.7, 3.4 and 3.6.
- Multi row update is not supported, see test/test_update.py for an example
Setup you python project and install sqlalchemy-exasol
> pip install sqlalchemy-exasol
for turbodbc support:
> pip install sqlalchemy-exasol[turbodbc]
Talk to EXASolution using SQLAlchemy
from sqlalchemy import create_engine e = create_engine("exa+pyodbc://A_USER:A_PASSWORD@192.168.1.2..8:1234/my_schema?CONNECTIONLCALL=en_US.UTF-8&driver=EXAODBC") r = e.execute("select 42 from dual").fetchall()
to use turbodbc as driver:
from sqlalchemy import create_engine e = create_engine("exa+turbodbc://A_USER:A_PASSWORD@192.168.1.2..8:1234/my_schema?CONNECTIONLCALL=en_US.UTF-8&driver=EXAODBC") r = e.execute("select 42 from dual").fetchall()
The dialect supports two connection urls for create_engine. A DSN (Data Source Name) mode and a host mode:
- SELECT, INSERT, UPDATE, DELETE statements
- you can even use the MERGE statement (see unit tests for examples)
- Schema name and parameters are optional for the host url string
- At least on Linux/Unix systems it has proven valuable to pass 'CONNECTIONLCALL=en_US.UTF-8' as a url parameter. This will make sure that the client process (Python) and the EXASOL driver (UTF-8 internal) know how to interpret code pages correctly.
- Always use all lower-case identifiers for schema, table and column names. SQLAlchemy treats all lower-case identifiers as case-insensitive, the dialect takes care of transforming the identifier into a case-insensitive representation of the specific database (in case of EXASol this is upper-case as for Oracle)
- As of EXASol client driver version 4.1.2 you can pass the flag 'INTTYPESINRESULTSIFPOSSIBLE=y' in the connection string (or configure it in your DSN). This will convert DECIMAL data types to Integer-like data types. Creating integers is a factor three faster in Python than creating Decimals.
To run the unit tests you need:
- set the default connection string in the setup.cfg file, which should contain an existing schema to run tests against. Note that the tests also use a schema "test_schema";
- set the DRIVER path under the EXAODBC section in the odbcconfig/odbcinst.ini file;
- set the ODBCINSTINI and ODBCINST environment variables to point to the full path of odbcconfig/odbcinst.ini
and finally run the unit tests:
$ py.test test/
The unixodbc Stack is not the most friendly for programmers. If you get strange errors from the driver mangager, you might have an issue with the names of the unixodbc libs. Have a look at https://github.com/blue-yonder/sqlalchemy_exasol/blob/master/fix_unixodbc_so.sh to find ideas on how to fix this on Ubuntu. Good luck!