Collectives™ on Stack Overflow
Find centralized, trusted content and collaborate around the technologies you use most.
Learn more about Collectives
Teams
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
Learn more about Teams
I have the following code, using pscyopg2:
sql = 'select %s from %s where utctime > %s and utctime < %s order by utctime asc;'
data = (dataItems, voyage, dateRangeLower, dateRangeUpper)
rows = cur.mogrify(sql, data)
This outputs:
select 'waterTemp, airTemp, utctime' from 'ss2012_t02' where utctime > '2012-05-03T17:01:35+00:00'::timestamptz and utctime < '2012-05-01T17:01:35+00:00'::timestamptz order by utctime asc;
When I execute this, it falls over - this is understandable, as the quotes around the table name are illegal.
Is there a way to legally pass the table name as a parameter, or do I need to do a (explicitly warned against) string concatenation, ie:
voyage = 'ss2012_t02'
sql = 'select %s from ' + voyage + ' where utctime > %s and utctime < %s order by utctime asc;'
Cheers for any insights.
According to the official documentation:
If you need to generate dynamically an SQL query (for instance
choosing dynamically a table name) you can use the facilities
provided by the psycopg2.sql module.
The sql module is new in psycopg2 version 2.7. It has the following syntax:
from psycopg2 import sql
cur.execute(
sql.SQL("insert into {table} values (%s, %s)")
.format(table=sql.Identifier('my_table')),
[10, 20])
More on: https://www.psycopg.org/docs/sql.html#module-usage
[Update 2017-03-24: AsIs should NOT be used to represent table or fields names, the new sql module should be used instead: https://stackoverflow.com/a/42980069/5285608 ]
Also, according to psycopg2 documentation:
Warning: Never, never, NEVER use Python string concatenation (+) or string parameters interpolation (%) to pass variables to a SQL query string. Not even at gunpoint.
–
–
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
–
–
–
–
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.
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):
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 ...
–
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), ))
–
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.
–
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
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.
–
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
