Обсуждение: How use input parameter as path to COPY in function?

I am missing something basic. How can I  use an input parameter as the
destination path in a COPY statement in a function. The following fails
with a syntax error at or near the parameter.

CREATE OR REPLACE FUNCTION  dvd.export_tables(IN export_path text)
RETURNS void
AS
$$
BEGIN
  copy dvd.genre to export_path
  with
  delimiter as E'\t'
  null as '';
END;
$$
  LANGUAGE 'plpgsql' VOLATILE

Bill Todd <pg@dbginc.com> writes:
> I am missing something basic. How can I  use an input parameter as the
> destination path in a COPY statement in a function.

plpgsql can only substitute parameter values into places where a data
value is called for in a DML statement (ie, SELECT/INSERT/UPDATE/DELETE).
To use a parameter in other contexts, such as a utility statement like
COPY, you need to construct the command as a string and EXECUTE it.
Try something like

   EXECUTE 'copy dvd.genre to ' || quote_literal(export_path) ||
    $q$
     with
     delimiter as E'\t'
     null as ''
    $q$ ;

(There's any number of ways to do the quoting here, of course,
but I do strongly recommend using quote_literal() on the parameter.)

            regards, tom lane

Thanks Tom. As usual, I learned a lot more from your reply than just the answer to my question .

Bill

Tom Lane wrote:

Bill Todd <pg@dbginc.com> writes: 

I am missing something basic. How can I  use an input parameter as the 
destination path in a COPY statement in a function.   

plpgsql can only substitute parameter values into places where a data
value is called for in a DML statement (ie, SELECT/INSERT/UPDATE/DELETE).
To use a parameter in other contexts, such as a utility statement like
COPY, you need to construct the command as a string and EXECUTE it.
Try something like
  EXECUTE 'copy dvd.genre to ' || quote_literal(export_path) ||   $q$    with    delimiter as E'\t'    null as ''   $q$ ;

(There's any number of ways to do the quoting here, of course,
but I do strongly recommend using quote_literal() on the parameter.)
		regards, tom lane