plpgsql Select statement in For loop to create multiple CSV files - postgresql

Question

I would like to repeat the following query 8760 times, replacing ‘2’ with 1 to 8760 for every hour in the year. The idea is to create a separate CSV file for each hour for further processing.
COPY
(SELECT *
FROM
public.completedsolarirad2012
WHERE
completedsolarirad2012."UniquetmstmpID" = 2)
TO 'C:\temp\2012hour2.csv' WITH DELIMITER ','
CSV HEADER
I have put together the following function (testing with only a few hours):
CREATE OR REPLACE FUNCTION everyhour()
RETURNS void AS
$BODY$BEGIN
FOR i IN 0..5 LOOP
EXECUTE $x$
COPY (
SELECT *
FROM
public.completedsolarirad2012
WHERE
completedsolarirad2012."UniquetmstmpID" = i
)
TO $concat$ 'C:\temp.' || i::text
|| '.out.csv' WITH DELIMITER ',' CSV HEADER $concat$
$x$;
END LOOP;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION everyhour()
OWNER TO postgres;
I seem to be having two separate problems:
Firstly, I’m getting:
Error: column "i" does not exist.
Secondly, when I test the concatenation statement only by replacing “i” with e.g. “2”, I get:
Error: relative path not allowed for COPY to file
I am the postgres superuser, so I do not understand why I am having this problem.
Note: Removing the $concat$ double-quoting around the concatenation statement gives the following error:
ERROR: syntax error at or near "||"
LINE 9: TO 'C:\temp.' || i::text
I would be very grateful for any help.

Answer 1

Assuming your server OS is Windows.
CREATE OR REPLACE FUNCTION everyhour()
RETURNS void AS
$func$
BEGIN
FOR i IN 0..5 LOOP
EXECUTE '
COPY (
SELECT *
FROM public.completedsolarirad2012 c
WHERE c."UniquetmstmpID" = ' || i || $x$)
TO 'C:/temp.'$x$ || i || $x$'.out.csv' WITH DELIMITER ',' CSV HEADER$x$;
END LOOP;
END
$func$ LANGUAGE plpgsql;
You had one layer of dollar-quoting too many.
You also accidentally concatenated the letter "i" instead of its value.
Use forward-slashes, even with windows. Or you may have to double up the backslashes, depending on your settings. More in this related answer:
PostgreSQL: export resulting data from SQL query to Excel/CSV
Simpler with format()
Since Postgres 9.1 you can use format() to simplify complex concatenations:
CREATE OR REPLACE FUNCTION everyhour()
RETURNS void AS
$func$
BEGIN
FOR i IN 0..5 LOOP
EXECUTE format($x$COPY (
SELECT *
FROM public.completedsolarirad2012 c
WHERE c."UniquetmstmpID" = %1$s)
TO 'C:/temp.%1$s.out.csv' WITH DELIMITER ',' CSV HEADER$x$, i);
END LOOP;
END
$func$ LANGUAGE plpgsql;