declare
	qstring text;
	number integer := 5;
	table text;
begin
	qstring := 'select * from R';
	qstring := qstring || ' where a ='||quote_literal(number);

	execute qstring into rec;

...

	table := 'R';
	qstring := 'select * from '||quote_ident(table);
	qstring := qstring|| ' where a ='||quote_literal(number);

	execute qstring into rec;
	
-- select * from R where a = '5'

	for rec in
		select * from R where a = number
	loop
		...
	end loop;

end;