Passing table name as a parameter in psycopg2

The table name cannot be passed as a parameter, but everything else can. Thus, the table name should be hard coded in your app (Don’t take inputs or use anything outside of the program as a name). The code you have should work for this.

On the slight chance that you have a legitimate reason to take an outside table name, make sure that you don’t allow the user to directly input it. Perhaps an index could be passed to select a table, or the table name could be looked up in some other way. You are right to be wary of doing this, however. This works, because there are relatively few table names around. Find a way to validate the table name, and you should be fine.

It would be possible to do something like this, to see if the table name exists. This is a parameterised version. Just make sure that you do this and verify the output prior to running the SQL code. Part of the idea for this comes from this answer.

SELECT 1 FROM information_schema.tables WHERE table_schema = 'public' and table_name=%s LIMIT 1

If you want to pass the table name as a parameter, you can use this wrapper:

class Literal(str):
    def __conform__(self, quote):
        return self

    @classmethod
    def mro(cls):
        return (object, )

    def getquoted(self):
        return str(self)

Usage: cursor.execute("CREATE TABLE %s ...", (Literal(name), ))

I have created a little utility for preprocessing of SQL statements with variable table (…) names:

from string import letters
NAMECHARS = frozenset(set(letters).union('.'))

def replace_names(sql, **kwargs):
    """
    Preprocess an SQL statement: securely replace table ... names
    before handing the result over to the database adapter,
    which will take care of the values.

    There will be no quoting of names, because this would make them
    case sensitive; instead it is ensured that no dangerous chars
    are contained.

    >>> replace_names('SELECT * FROM %(table)s WHERE val=%(val)s;',
    ...               table='fozzie')
    'SELECT * FROM fozzie WHERE val=%(val)s;'
    """
    for v in kwargs.values():
        check_name(v)
    dic = SmartDict(kwargs)
    return sql % dic

def check_name(tablename):
    """
    Check the given name for being syntactically valid,
    and usable without quoting
    """
    if not isinstance(tablename, basestring):
        raise TypeError('%r is not a string' % (tablename,))
    invalid = set(tablename).difference(NAMECHARS)
    if invalid:
        raise ValueError('Invalid chars: %s' % (tuple(invalid),))
    for s in tablename.split('.'):
        if not s:
            raise ValueError('Empty segment in %r' % tablename)

class SmartDict(dict):
    def __getitem__(self, key):
        try:
            return dict.__getitem__(self, key)
        except KeyError:
            check_name(key)
            return key.join(('%(', ')s'))

The SmartDict object returns %(key)s for every unknown key, preserving them for the value handling. The function could check for the absence of any quote characters, since all quoting now should be taken care of …

Per this answer you can do it as so:

import psycopg2
from psycopg2.extensions import AsIs

#Create your connection and cursor...

cursor.execute("SELECT * FROM %(table)s", {"table": AsIs("my_awesome_table")})

You can just use the module format for the table name and then use the regular paramaterization for the execute:

xlist = (column, table)
sql = 'select {0} from {1} where utctime > %s and utctime < %s order by utctime asc;'.format(xlist)

Keep in mind if this is exposed to the end user, you will not be protected from SQL injection unless you write for it.

Surprised no one has mentioned doing this:

sql = 'select {} from {} where utctime > {} and utctime < {} order by utctime asc;'.format(dataItems, voyage, dateRangeLower, dateRangeUpper)
rows = cur.mogrify(sql)

format puts in the string without quotations.

This is a workaround I have used in the past

query = "INSERT INTO %s (col_1, col_2) VALUES (%%s, %%s)" % table_name
cur.execute(query, (col_1_var, col_2_var))

Hope it help 🙂

This is a small addition to @Antoine Dusséaux’s answer. If you want to pass two (unquoted) parameters in a SQL query, you can do it as follows: –

query = sql.SQL("select {field} from {table} where {pkey} = %s").format(
    field=sql.Identifier('my_name'),
    table=sql.Identifier('some_table'),
    pkey=sql.Identifier('id'))

As per the documentation,

Usually you should express the template of your query as an SQL
instance with {}-style placeholders and use format() to merge the
variable parts into them, all of which must be Composable subclasses.
You can still have %s-style placeholders in your query and pass values
to execute(): such value placeholders will be untouched by format()

Source: https://www.psycopg.org/docs/sql.html#module-usage

Also, please keep this in mind while writing queries.

If you need to pass a qualified identifier, e.g. a schema name + a table name:

from psycopg2 import sql

cur.execute(
    sql.SQL(
        "INSERT INTO {table} VALUES (%s, %s)"
    ).format(
        table=sql.Identifier("my_schema", "my_table")
    ),
    [10, 20]
)

# INSERT INTO "my_schema"."my_table" VALUES (10, 20)

See: https://www.psycopg.org/docs/sql.html#psycopg2.sql.Identifier