COPY command: copy only specific columns from csv

Question

I had a question surrounding the COPY command in PostgreSQL. I have a CSV file that I only want to copy some of the columns values into my PostgreSQL table.

Is it possible to do this? I am familiar with using the COPY command to copy all of the data from a CSV into a table using the header to map to the column names but how is this possible when I only want some of the columns?

Answer 1

Either pre-process the CSV file, or (what I probably would do) import into a temporary copy of the target table and INSERT only selected columns in a second step:

CREATE TEMP TABLE tmp AS SELECT * FROM target_table LIMIT 0;
ALTER TABLE tmp ADD COLUMN etra_column1 text
             ,  ADD COLUMN etra_column2 text;  -- add excess columns
COPY tmp FROM '/path/tp/file.csv';

INSERT INTO target_table (col1, col2, col3)
SELECT col1, col2, col3 FROM tmp  -- only reelvant columns
WHERE  ...  -- optional, to also filter rows

A temporary table is dropped automatically at the end of the session. If the processing takes longer, use a regular table.

Answer 2

COPY target_table FROM PROGRAM 'cut -f1,2,3 -d, /path/tp/file.csv';