fabien_fdw.py

import csv
import io

from multicorn import ForeignDataWrapper


class FileCsvForeignDataWrapper(ForeignDataWrapper):
    def __init__(self, options, columns):
        super(FileCsvForeignDataWrapper, self).__init__(options, columns)
        self.options = options
        self.columns = columns

    def execute(self, quals, columns):
        has_header = self.options.get('header', 'false') == 'true'


        with io.open(self.options["path"], 'r') as filep:
            reader = csv.reader(filep, delimiter=self.options.get("delimiter", ","))
            for i, line in enumerate(reader):
                if i == 0 and not has_header:
                    continue

                row = {}
                for i, column_name in enumerate(self.columns):
                    row[column_name] = line[i]
                yield row

file1.csv

sql.sql

CREATE EXTENSION multicorn

CREATE SERVER file_csv foreign data wrapper multicorn options (
    wrapper 'fabien_fdw.FileCsvForeignDataWrapper'
);

CREATE FOREIGN TABLE file1 (
    A character varying,
    B character varying
) server file_csv options (path '/data/file1.csv');

select a from file1
select * from file1 where A = '1';
EXPLAIN  select * from file1 where A='1';