How to ignore errors with psql \copy meta-command

Question

I am using psql with a PostgreSQL database and the following copy command:

\COPY isa (np1, np2, sentence) FROM 'c:\Downloads\isa.txt' WITH DELIMITER '|'

I get:

ERROR:  extra data after last expected column

How can I skip the lines with errors?

Answer 1

It is too bad that in 25 years Postgres doesn't have -ignore-errors flag or option for COPY command. In this era of BigData you get a lot of dirty records and it can be very costly for the project to fix every outlier.

I had to make a work-around this way:

1. Copy the original table and call it dummy_original_table
2. in the original table, create a trigger like this:

    CREATE OR REPLACE FUNCTION on_insert_in_original_table() RETURNS trigger AS  $$  
    DECLARE
        v_rec   RECORD;
    BEGIN
        -- we use the trigger to prevent 'duplicate index' error by returning NULL on duplicates
        SELECT * FROM original_table WHERE primary_key=NEW.primary_key INTO v_rec;
        IF v_rec IS NOT NULL THEN
            RETURN NULL;
        END IF; 
        BEGIN 
            INSERT INTO original_table(datum,primary_key) VALUES(NEW.datum,NEW.primary_key)
                ON CONFLICT DO NOTHING;
        EXCEPTION
            WHEN OTHERS THEN
                NULL;
        END;
        RETURN NULL;
    END;

3. Run a copy into the dummy table. No record will be inserted there, but all of them will be inserted in the original_table

psql dbname -c \copy dummy_original_table(datum,primary_key) FROM '/home/user/data.csv' delimiter E'\t'

Answer 2

Here's one solution -- import the batch file one line at a time. The performance can be much slower, but it may be sufficient for your scenario:

#!/bin/bash

input_file=./my_input.csv
tmp_file=/tmp/one-line.csv
cat $input_file | while read input_line; do
    echo "$input_line" > $tmp_file
    psql my_database \
     -c "\
     COPY my_table \
     FROM `$tmp_file` \
     DELIMITER '|'\
     CSV;\
    "
done

Additionally, you could modify the script to capture the psql stdout/stderr and exit status, and if the exit status is non-zero, echo $input_line and the captured stdout/stderr to stdin and/or append it to a file.

Answer 3

Workaround: remove the reported errant line using sed and run \copy again

Later versions of Postgres (including Postgres 13), will report the line number of the error. You can then remove that line with sed and run \copy again, e.g.,

#!/bin/bash
bad_line_number=5  # assuming line 5 is the bad line
sed ${bad_line_number}d < input.csv > filtered.csv

[per the comment from @Botond_Balázs ]