Essential SQLAlchemy

Chapter 5. Running Queries and Updates

SQLAlchemy provides a rich Pythonic interface for constructing SQL updates and queries, known as the SQL Expression Language. This language is based around the concept of an SQL statement, which represents some database-independent SQL syntax that may have one or more bind variables, and that can be executed on an SQL Engine or other Connectable. This chapter introduces the various kinds of data manipulation supported by SQLAlchemy (SQL INSERT, UPDATE, and DELETE) and performed on the query interface (SQL SELECT).

Inserts, Updates, and Deletes

Insert, Update, and Delete constructs are created in SQLAlchemy via the Table methods insert, update, and delete, or via the insert, update, and delete functions. The functionality of these data manipulation language (DML) constructs is equivalent, regardless of whether they are constructed via methods or functions; the distinction is a question of style more than substance.

Although each DML construct has its own particulars regarding construction, they all end up generating a Statement. We can inspect the SQL text corresponding to the statement by printing it out:

>>> metadata=MetaData()
>>> 
>>> simple_table = Table(
...     'simple', metadata,
...     Column('id', Integer, primary_key=True),
...     Column('col1', Unicode(20)))
>>> 
>>> stmt = simple_table.insert()
>>> print stmt
INSERT INTO simple (id, col1) VALUES (:id, :col1)

Note in the previous example that SQLAlchemy has created bind parameters for each of the ...