On Thu, Jun 27, 2013 at 11:01 AM, Burak Arslan
<[email protected]> wrote:
> Hi,
>
> First, some background:
>
> psql (9.2.4)
> Type "help" for help.
>
> somedb=# create table a(a varchar(5));
> CREATE TABLE
> somedb=# insert into a values (E'\\');
> INSERT 0 1
> somedb=# select * from a where a = '\';
> a
> ---
> \
> (1 row)
>
> somedb=# select * from a where a like '\';
> ERROR: LIKE pattern must not end with escape character
> somedb=# select * from a where a like '\\';
> a
> ---
> \
> (1 row)
>
> somedb=# select * from a where a like E'\\\\';
> a
> ---
> \
> (1 row)
>
> Here's the relevant part of the documentation:
>
> http://www.postgresql.org/docs/9.2/static/functions-matching.html
> Section 9.7.1
>
> So I guess we can safely say that it's a known and documented behaviour
> and won't be considered to be a bug by the postgres team.
>
> http://www.postgresql.org/docs/9.1/static/release-9-1.html Section
> E.10.2.1 could also be slightly (as it says nothing about LIKE) relevant.
>
> Here's what happens with sqlalchemy:
>
> Python 3.3.2 (default, May 23 2013, 10:38:22)
> [GCC 4.6.3] on linux
> Type "help", "copyright", "credits" or "license" for more information.
>>>> import sqlalchemy
>>>> sqlalchemy.__version__
> '0.8.1'
>>>> from sqlalchemy import MetaData, create_engine
>>>> e = create_engine("postgres://postgres:@localhost:5432/somedb")
>>>> meta = MetaData(bind=e)
>>>> meta.reflect()
>>>> t=meta.tables['a']
>>>> e.execute(t.select(t.c.a.like('\\')))
> Traceback (most recent call last):
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 867, in _execute_context
> context)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/default.py",
> line 326, in do_execute
> cursor.execute(statement, parameters)
> psycopg2.DataError: LIKE pattern must not end with escape character
>
>
> The above exception was the direct cause of the following exception:
>
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 1614, in execute
> return connection.execute(statement, *multiparams, **params)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 662, in execute
> params)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 761, in _execute_clauseelement
> compiled_sql, distilled_params
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 874, in _execute_context
> context)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 1024, in _handle_dbapi_exception
> exc_info
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/util/compat.py",
> line 155, in raise_from_cause
> reraise(type(exception), exception, tb=exc_tb, cause=exc_value)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/util/compat.py",
> line 150, in reraise
> raise value.with_traceback(tb)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/base.py",
> line 867, in _execute_context
> context)
> File
> "/home/plq/.local/lib64/python3.3/site-packages/SQLAlchemy-0.8.1-py3.3.egg/sqlalchemy/engine/default.py",
> line 326, in do_execute
> cursor.execute(statement, parameters)
> sqlalchemy.exc.DataError: (DataError) LIKE pattern must not end with
> escape character
> 'SELECT a.a \nFROM a \nWHERE a.a LIKE %(a_1)s' {'a_1': '\\'}
>>>>
>
> Anything else I can do to help?
>
Remember that Python also has its own string escaping. When you write
a literal '\\' in Python, you are creating a string containing a
single backslash. If you want to pass 2 backslashes to PG, you either
need to use 4 slashes in Python ("\\\\"), or use a raw string (r"\\")
>>> print '\\'
\
>>> print '\\\\'
\\
>>> print r'\\'
\\
Hope that helps,
Simon
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