To ignore duplicate keys during 'copy from' in postgresql

I have to dump large amount of data from file to a table PostgreSQL. I know it does not support 'Ignore' 'replace' etc as done in MySql. Almost all posts regarding this in the web suggested the same thing like dumping the data to a temp table and then do a 'insert ... select ... where not exists...'.

This will not help in one case, where the file data itself contained duplicate primary keys. Any body have an idea on how to handle this in PostgreSQL?

P.S. I am doing this from a java program, if it helps

Solution 1:

Use the same approach as you described, but DELETE (or group, or modify ...) duplicate PK in the temp table before loading to the main table.

Something like:

CREATE TEMP TABLE tmp_table 
ON COMMIT DROP
AS
SELECT * 
FROM main_table
WITH NO DATA;

COPY tmp_table FROM 'full/file/name/here';

INSERT INTO main_table
SELECT DISTINCT ON (PK_field) *
FROM tmp_table
ORDER BY (some_fields)

Details: CREATE TABLE AS, COPY, DISTINCT ON

Solution 2:

PostgreSQL 9.5 now has upsert functionality. You can follow Igor's instructions, except that final INSERT includes the clause ON CONFLICT DO NOTHING.

INSERT INTO main_table
SELECT *
FROM tmp_table
ON CONFLICT DO NOTHING

Solution 3:

Igor’s answer helped me a lot, but I also ran into the problem Nate mentioned in his comment. Then I had the problem—maybe in addition to the question here—that the new data did not only contain duplicates internally but also duplicates with the existing data. What worked for me was the following.

CREATE TEMP TABLE tmp_table AS SELECT * FROM newsletter_subscribers;
COPY tmp_table (name, email) FROM stdin DELIMITER ' ' CSV;
SELECT count(*) FROM tmp_table;  -- Just to be sure
TRUNCATE newsletter_subscribers;
INSERT INTO newsletter_subscribers
    SELECT DISTINCT ON (email) * FROM tmp_table
    ORDER BY email, subscription_status;
SELECT count(*) FROM newsletter_subscribers;  -- Paranoid again

Both internal and external duplicates become the same in the tmp_table and then the DISTINCT ON (email) part removes them. The ORDER BY makes sure that the desired row comes first in the result set and DISTINCT then discards all further rows.