On 2025/06/09 16:10, Shinya Kato wrote:
Hi hackers, I'd like to propose a new feature for the COPY FROM command to allow skipping multiple header lines when loading data. This enhancement would enable files with multi-line headers to be loaded without any preprocessing, which would significantly improve usability. In real-world scenarios, it's common for data files to contain multiple header lines, such as file descriptions or column explanations. Currently, the COPY command cannot load these files directly, which requires users to preprocess them with tools like sed or tail. Although you can use "COPY t FROM PROGRAM 'tail -n +3 /path/to/file'", some environments do not have the tail command available. Additionally, this approach requires superuser privileges or membership in the pg_execute_server_program role. This feature also has precedent in other major RDBMS: - MySQL: LOAD DATA ... IGNORE N LINES [1] - SQL Server: BULK INSERT … WITH (FIRST ROW=N) [2] - Oracle SQL*Loader: sqlldr … SKIP=N [3] I have not yet created a patch, but I am willing to implement an extension for the HEADER option. I would like to discuss the specification first. The specification I have in mind is as follows: - Command: COPY FROM - Formats: text and csv - Option syntax: HEADER [ boolean | integer | MATCH] (Extend the HEADER option to accept an integer value in addition to the existing boolean and MATCH keywords.) - Behavior: Let N be the specified integer. - If N < 0, raise an error. - If N = 0 or 1, same behavior when boolean is specified. - If N > 1, skip the first N rows. Thoughts?
I generally like the idea. However, a similar proposal was made earlier [1], and seemingly some hackers weren't in favor of it. It's probably worth reading that thread to understand the previous concerns. Regards, [1] https://postgr.es/m/calay4q8ngsxp0p5uf56vn-md7rewqzp5k6ps1cgum26x4fs...@mail.gmail.com -- Fujii Masao NTT DATA Japan Corporation
