Copy NULL values present in csv file to postgres

1st Replace all NULL with ' ' (Space).

Then COPY r FROM '/home/y.csv' WITH DELIMITER ',' NULL as ' ' CSV;

Have you tried it?

 copy r from '/home/y.csv' delimiter ',' csv WITH NULL AS 'null';

The error is because you are inserting NULL as string. Remove the quotes around NULL and it should work.

after giving the path of the file, we need to use 'With' before adding other paramters -

copy r from '/home/y.csv' with delimiter ',' NULL AS 'null' csv header;