Passing list of parameters to SQL in psycopg2

Question

I have a list of ids of rows to fetch from database. I’m using python and psycopg2, and my problem is how to effectively pass those ids to SQL? I mean that if I know the length of that list, it is pretty easy because I can always manually or automatically add as many “%s” expressions into query string as needed, but here I don’t know how much of them I need. It is important that I need to select that rows using sql “id IN (id1, id2, …)” statement. I know that it is possible to check the length of the list and concatenate suitable number of “%s” into query string, but I’m afraid that it would be very slow and ugly. Does anyone have an idea on how to solve it? And please don’t ask why I need to do it with “IN” statement – it is a benchmark which is a part of my class assignment. Thanks in advance!

Asked By: k_wisniewski

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Source

Answer 1

Python tuples are converted to sql lists in psycopg2:

cur.mogrify("SELECT * FROM table WHERE column IN %s;", ((1,2,3),))

would output

'SELECT * FROM table WHERE column IN (1,2,3);'

For Python newcomers: It is unfortunately important to use a tuple, not a list here. Here’s a second example:

cur.mogrify("SELECT * FROM table WHERE column IN %s;", 
    tuple([row[0] for row in rows]))

Answered By: philofinfinitejest

Answer 2

this question is old and maybe there is a newer one out there, but the answer my colleagues are going with right now is this:

sql = "SELECT * FROM table WHERE column = ANY(%(parameter_array)s)"
cur.execute(sql,{"parameter_array": [1, 2, 3]})

Answered By: Brandon Henry

Answer 3

Now sql module of psycopg2 (https://www.psycopg.org/docs/sql.html) can be used to safeguard against errors and injections, like e.g.:

import psycopg2
from psycopg2 import sql

params = config()
conn = psycopg2.connect(**params)
cur = conn.cursor()

ids = ['a','b','c']
sql_query = sql.SQL('SELECT * FROM {} WHERE id IN ({});').format(
                    sql.Identifier('table_name'),
                    sql.SQL(',').join(map(sql.Literal, ids))
                )
print (sql_query.as_string(cur)) # for debug
cur.execute(sql_query)

from configparser import ConfigParser
def config(filename='database.ini', section='postgresql'):
    # create a parser
    parser = ConfigParser()
    # read config file
    parser.read(filename)

    # get section, default to postgresql
    db = {}
    if parser.has_section(section):
        params = parser.items(section)
        for param in params:
            db[param[0]] = param[1]
    else:
        raise Exception('Section {0} not found in the {1} file'.format(section, filename))

    return db

Note: sql.Identifier will add quotes if needed so it will work if you use quoted identifiers in PostgreSQL also (they have to be used to allow e.g. case sensitive naming).

Example and structure of database.ini:

[postgresql]
host=localhost
port=5432
database=postgres
user=user
password=mypass

Answered By: Alexei Martianov

Passing list of parameters to SQL in psycopg2

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