Python/psycopg2 WHERE IN statement

问题:

What is the correct method to have the list (countryList) be available via %s in the SQL statement?

# using psycopg2
countryList=['UK','France']

sql='SELECT * from countries WHERE country IN (%s)'
data=[countryList]
cur.execute(sql,data)

As it is now, it errors out after trying to run "WHERE country in (ARRAY[...])". Is there a way to do this other than through string manipulation?

Thanks

回答1:

For the IN operator, you want a tuple instead of list, and remove parentheses from the SQL string.

# using psycopg2
data=('UK','France')

sql='SELECT * from countries WHERE country IN %s'
cur.execute(sql,(data,))

During debugging you can check that the SQL is built correctly with

cur.mogrify(sql, (data,))

回答2:

To expland on the answer a little and to address named parameters, and converting lists to tuples:

countryList = ['UK', 'France']

sql = 'SELECT * from countries WHERE country IN %(countryList)s'

cur.execute(sql, { # You can pass a dict for named parameters rather than a tuple. Makes debugging hella easier.
    'countryList': tuple(countryList), # Converts the list to a tuple.
})

回答3:

You could use a python list directly as below. It acts like the IN operator in SQL and also handles a blank list without throwing any error.

data=['UK','France']
sql='SELECT * from countries WHERE country = ANY (%s)'
cur.execute(sql,(data,))

source: http://initd.org/psycopg/docs/usage.html#lists-adaptation