Re: [sqlalchemy] bindparams fails for the table

[Michael Bayer]

a SQL statement cannot use a bound parameter as a substitute for SQL identifiers, such as table and column names.

that is, this is not valid:

conn.execute(“select * from :table”, table=‘foo’)

bound parameters are only intended for literal values used in SQL expressions, that is, the *data*, not the *structure* of the statement.  This is not a SQLAlchemy limitation, it’s a fundamental behavior of the DBAPI and database client systems in general.   Some DBAPIs might allow arbitrary substitutions, but if they do, they’re buggy.   

If you have the table name as dynamic, then the approach you have doing the substitution using standard Python string techniques is appropriate.

On May 15, 2014, at 5:17 AM, goo...@cornelinux.de wrote:

Hi,

my program tries to read data from a configurable, unknown user table.
So I came up with such a statement:

        result = self.session.execute("SELECT * FROM :mytable", {"mytable": self.table})

But when I run it, I get this, what I do not understand:

    result = self.session.execute("SELECT * FROM :mytable", {"mytable": "wp_users"})
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 791, in execute
    clause, params or {})
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1405, in execute
    params)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1538, in _execute_clauseelement
    compiled_sql, distilled_params
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1646, in _execute_context
    context)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1639, in _execute_context
    context)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 330, in do_execute
    cursor.execute(statement, parameters)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 174, in execute
    self.errorhandler(self, exc, value)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
sqlalchemy.exc.ProgrammingError: (ProgrammingError) (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''wp_users'' at line 1") 'SELECT * FROM %s' ('wp_users',)


Something like this works out:

        t = "SELECT * from %s" % self.table
        result = self.session.execute(t)

But I do not not not want to do this, since I do not want to check the self.table variable... ;-)
I am running ubuntu 12.04 with old sqla 0.7.4.

Thanks a lot and kind regards
Cornelius

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