did you check this?
https://groups.google.com/forum/?fromgroups=#!topic/sqlalchemy/VXXB12-3JCY
Also, a comparison between Django ORM and SQL Alchemy :
http://blog.mathieu-leplatre.info/sqlalchemy-a-brave-new-world.html
Pasting the response form the above google groups link:
Mark Erbaugh 22/11/2010
I don't have any example code, but I have written several Python applications (and one C++ app) using plain SQL and have
started work on a new app using SQLAlchemy, so I'll share my
experience.
Let me add that I spent several years maintaining a moderately sized
SQL database and wrote lots of pure SQL, though not necessarily using
Python.
As my programs accessed SQL, I found myself writing a lot of SQL code
to access the data. A lot of this code while not identical, was very
similar and seemed redundant. For example, take a simple single table
lookup. If you want to do simple CRUD (create, update & delete), you
have to write at least three separate SQL statements for each table.
While the skeleton of these SQL statements are similar, the specific
column names and the table name are different. I ended up writing some
Python routines that would build the SQL statements if I supplied a
list of columns and the table name. But this is what SQLAlchemy does
(and much more) so why reinvent the wheel?
In the case of my C++ app (I hadn't found a suitable ORM), I ended up
writing a Python script to generate SQL statements and C++ code to
access the tables.
Another advantage is the relative ease with which you can handle
changes to the database structure. As I was developing my SA app, I
realized that I needed a new column in (at least) one of my tables.
I'm using SA's declarative approach and I only had to add the column
to my declarative. I didn't have to change any SQL or Python code.
One "problem" I have had with SQLAlchemy is unlearning the way I did
things with pure SQL. At it's simplest level, SQLAlchemy can generate
the SQL and Python code to access single tables and you might be
tempted to write Python code to merge this kind of single table access
into larger data graphs, but the true power (IMHO) of SQLAlchemy is
that it can handle complex data graphs automatically.
Mark