/*до рефакторинга*/
EXPLAIN
SELECT *
  FROM public.salesorder AS t1
 WHERE EXTRACT(YEAR FROM orderdate) = 2006
   AND EXTRACT(MONTH FROM orderdate) = 7

/*после рефакторинга*/
EXPLAIN
SELECT *
  FROM public.salesorder AS t1
 WHERE orderdate BETWEEN '2006-07-01 00:00:00'::TIMESTAMP
                     AND '2006-07-31 00:00:00'::TIMESTAMP

/*до рефакторинга*/
EXPLAIN
SELECT COUNT(DISTINCT t1.orderid)
  FROM public.salesorder AS t1
  JOIN public.orderdetail AS t2
    ON t1.orderid = t2.orderid

/*после рефакторинга*/
EXPLAIN
SELECT COUNT(DISTINCT t1.orderid)
  FROM public.salesorder AS t1
 WHERE EXISTS(
               SELECT NULL
                 FROM public.orderdetail AS t2
                WHERE t1.orderid = t2.orderid)

/*до рефакторинга*/
EXPLAIN
SELECT SUM(CASE WHEN num % 3 = 0 THEN 1 END) AS foo,
       SUM(CASE WHEN num % 5 = 0 THEN 1 END) AS bar,
       SUM(CASE WHEN num % 3 = 0 AND num % 5 = 0 THEN 1 END) AS foobar
  FROM table1

/*после рефакторинга*/
EXPLAIN
SELECT COUNT(*) FILTER(WHERE num % 3 = 0) AS foo,
       COUNT(*) FILTER(WHERE num % 5 = 0) AS bar,
       COUNT(*) FILTER(WHERE num % 3 = 0 AND num % 5 = 0) AS foobar
  FROM table1