CREATE FUNCTION "URX_PUBLIC"."_add_raster_constraint_scale"(rastschema name, rasttable name, rastcolumn name, axis character) 
 RETURNS boolean AS 
$BODY$
	DECLARE
		fqtn text;
		cn name;
		sql text;
		attr double precision;
	BEGIN
		IF lower($4) != 'x' AND lower($4) != 'y' THEN
			RAISE EXCEPTION 'axis must be either "x" or "y"';
			RETURN FALSE;
		END IF;

		fqtn := '';
		IF length($1) > 0 THEN
			fqtn := quote_ident($1) || '.';
		END IF;
		fqtn := fqtn || quote_ident($2);

		cn := 'enforce_scale' || $4 || '_' || $3;

		sql := 'SELECT st_scale' || $4 || '('
			|| quote_ident($3)
			|| ') FROM '
			|| fqtn
			|| ' LIMIT 1';
		BEGIN
			EXECUTE sql INTO attr;
		EXCEPTION WHEN OTHERS THEN
			RAISE NOTICE 'Unable to get the %-scale of a sample raster: % (%)',
        upper($4), SQLERRM, SQLSTATE;
			RETURN FALSE;
		END;

		sql := 'ALTER TABLE ' || fqtn
			|| ' ADD CONSTRAINT ' || quote_ident(cn)
			|| ' CHECK (round(st_scale' || $4 || '('
			|| quote_ident($3)
			|| ')::numeric, 10) = round(' || text(attr) || '::numeric, 10))';
		RETURN  "URX_PUBLIC"._add_raster_constraint(cn, sql);
	END;
	$BODY$
 LANGUAGE 'plpgsql' VOLATILESTRICT ;