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Asked: 2026-05-22T18:29:24+00:00

I’m going through this SQLAlchemy tutorial and have become very confused by the following

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I’m going through this SQLAlchemy tutorial and have become very confused by the following example (about halfway down the page):

>>> s = select([(users.c.fullname + ", " + addresses.c.email_address).label('title')],
...        and_(
...            users.c.id==addresses.c.user_id,
...            users.c.name.between('m', 'z'),
...           or_(
...              addresses.c.email_address.like('%@aol.com'),
...              addresses.c.email_address.like('%@msn.com')
...           )
...        )
...    )
>>> print conn.execute(s).fetchall() 
SELECT users.fullname || ? || addresses.email_address AS title
FROM users, addresses
WHERE users.id = addresses.user_id AND users.name BETWEEN ? AND ? AND
(addresses.email_address LIKE ? OR addresses.email_address LIKE ?)
(', ', 'm', 'z', '%@aol.com', '%@msn.com')
[(u'Wendy Williams, wendy@aol.com',)]

How does (users.c.fullname + ", " + addresses.c.email_address) identify columns to select from– doesn’t that mean it looks for columns titled "fullname, email_address"? I’m clearly misunderstanding something. The result [(u'Wendy Williams, wendy@aol.com',)] is the same format as the string given to SELECT.. I just don’t understand how that works.

Never done databases before; I’m learning SQLAlchemy at the same time I’m learning SQL, so it’s entirely possible my problem is with SQL not SQLAlchemy.

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1 Answer

  1. Editorial Team

    users.c.fullname is a clever object that overloads the + operator. users.c.fullname + ", " creates a ClauseElement representing the expression, which SQLAlchemy knows how to translate to any SQL engine’s syntax. Same reason you can do users.c.name.between('m', 'z'); users.c.name is an object with a between method that returns a ClauseElement.

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