How do you pass a parameter to a pgsql command within a function?

Question

I use the copy function in postgresql often and I thought I'd create a function to make use of it. So let's say i have the following table

create table users
(
   userid serial primary key,
   prefix varchar(10) not null,
   firstname varchar(255) not null,
   lastname varchar(255) not null,
   email varchar(500) not null,
   password varchar(255) not null,
   created timestamp not null,
   modified timestamp not null
);

and the following function

create function getUsersCSV(  )
RETURNS void AS
$BODY$
  BEGIN
    COPY (select * from users) 
    TO 'c:\temp\users.csv' 
    WITH HEADER 
    CSV QUOTE '"' DELIMITER ',';
  END
$BODY$
LANGUAGE PLPGSQL;

function works but if I change the function to

create function getUsersCSV( filepath varchar )
RETURNS void AS
$BODY$
  BEGIN
    COPY (select * from users) 
    TO filepath 
    WITH HEADER 
    CSV QUOTE '"' DELIMITER ',';
  END
$BODY$
LANGUAGE PLPGSQL;

it throws the following syntax error ERROR: syntax error at or near "filepath" SQL state: 42601

Is there anyway to parameterize the destination value of the copy command?

Answer 1

You could do it with execute :

create function get_users_csv(filepath text) returns void as $$
declare
    cp_cmd text;
begin
    cp_cmd := 'copy (select * from users) to '
           || quote_literal(filepath)
           || ' with header csv quote ''"'' delimiter '',''';
    execute cp_cmd;
end;
$$ language plpgsql;

Don't forget to use quote_literal on your filepath just in case. You could also use dollar-quoting if you don't like all the doubled single quotes:

create function get_users_csv(filepath text) returns void as $$
declare
    cp_cmd text;
begin
    cp_cmd := $q$copy (select * from users) to $q$
           || quote_literal(filepath)
           || $q$ with header csv quote '"' delimiter ','$q$;
    execute cp_cmd;
end;
$$ language plpgsql;

But I find dollar quoting to be rather ugly for anything other than blocks of text.