PostgreSQL ON CONFLICT error inserting column EXCLUDED.column_name does not exist with psycopg2.sql Placeholders - sql

Question

I'm using psycopg2 with psycopg2.sql.
import psycopg2
from psycopg2 import sql
I re-wrote some static sql code to be more dynamic by using sql.Placeholder and sql.Identifier.
However, even when there is no conflict, I get an error:
Error inserting into table: column "EXCLUDED.domain_name" does not exist
My sql query looks like this:
query = sql.SQL("insert into dns ({}) values ({}) "
"ON CONFLICT ({}) "
"DO UPDATE SET ({}) = ({}) "
"WHERE {} >= ({});").format(
sql.SQL(', ').join(map(sql.Identifier, dns_cols)),
sql.SQL(', ').join(sql.Placeholder() * len(dns_vals)),
sql.SQL(', ').join(map(sql.Identifier, conflict_cols)),
sql.SQL(', ').join(map(sql.Identifier, dns_cols)),
sql.SQL(', ').join(map(sql.Identifier, excluded_names)),
sql.Identifier('EXCLUDED.updated_date_time'),
sql.Identifier('dns.updated_date_time')
)
mogrify prints out the following:
b'insert into dns ("domain_name", "tld", "subdomain", "https", "cf_url", "updated_date_time") values (\'example\', \'org\', \'\', false, \'http://example.org\', \'2018-12-06 23:12:00\') ON CONFLICT ("domain_name", "tld", "subdomain") DO UPDATE SET ("domain_name", "tld", "subdomain", "https", "cf_url", "updated_date_time") = ("EXCLUDED.domain_name", "EXCLUDED.tld", "EXCLUDED.subdomain", "EXCLUDED.https", "EXCLUDED.cf_url", "EXCLUDED.updated_date_time") WHERE "EXCLUDED.updated_date_time" >= ("dns.updated_date_time");'
dns_cols, excluded_names, and dns_vals are all lists and their values appear to be showing up just fine in the mogrify print out.
I have never needed to create EXCLUDED columns, they are always accessible when "ON CONFLICT" is triggered.
How do I reference EXCLUDED columns when using psycopg2.sql Placeholders?

Answer 1

You are referencing an unqualified column whose name contains a literal period. If you want to quote this, you would have to quote the two parts separately, not together. Also, EXCLUDED has to be in lower case if you do quote it (I am kind of surprised that it works at all when quoted).
"excluded"."domain_name"
The best way to do this is probably to hard code the EXCLUDED into the query string and remove it from the sql.Identifier call:
"DO UPDATE SET ({}) = (EXCLUDED.{}) "
...
sql.Identifier('updated_date_time'),