如何将变量传递给 Postgresql 中的复制命令

Question

I tried to make a variable in SQL statement in Postgresql, but it did not work. There are many csv files stored under the path. I want to set path in Postgresql that can tell copy command where can find csv files.

SQL statement sample:

\set outpath '/home/clients/ats-dev/'
\COPY licenses (_id, name,number_seats ) FROM :outpath + 'licenses.csv' CSV HEADER DELIMITER ',';
\COPY uploaded_files (_id, added_date ) FROM :outpath + 'files.csv' CSV HEADER DELIMITER ',';

It did not work. I got error: no such files. The two files licneses.csv and files.csv are stored under /home/cilents/ats-dev on Ubuntu. I found some sultion that use "\set file 'license.csv'". It did not work for me becacuse I have many csv files. also I tried to use "from: outpath || 'licenses.csv'". it did not work ether. Appreciate for any helps.

Using 9.3.

Answer 1

It looks like psql does not support :variable substitution within psql backslash commands.

test=> \set somevar fred
test=> \copy z from :somevar
:somevar: No such file or directory

so you will need to do this via an external tool like the unix shell. eg

for f in *.sql; do
    psql -c "\\copy $(basename $f) FROM '$f'"
done

Answer 2

You can try COPY command

\set outpath '\'/home/clients/ats-dev/'
COPY licenses (_id, name,number_seats ) FROM :outpath/licenses.csv' WITH CSV HEADER DELIMITER ',';
COPY uploaded_files (_id, added_date ) FROM :outpath/files.csv' WITH CSV HEADER DELIMITER ',';

Note: Files named in a COPY command are read or written directly by the server, not by the client application. Therefore, they must reside on or be accessible to the database server machine, not the client. They must be accessible to and readable or writable by the PostgreSQL user (the user ID the server runs as), not the client. Similarly, the command specified with PROGRAM is executed directly by the server, not by the client application, must be executable by the PostgreSQL user. COPY naming a file or command is only allowed to database superusers, since it allows reading or writing any file that the server has privileges to access.

Documentation: Postgresql 9.3 COPY

Answer 3

It may have been true when this was originally asked, that psql backslash commands didn't support variable interpolation, but in my PostgreSQL 14 instance that's no longer the case. However, the psql manpage is clear that \copy specifically does not support variable interpolation.