Amazon RedshiftがQUALIFY句をサポート
分析（Window）関数の利便性大向上！

create table store_sales (
    ss_sold_date date, 
    ss_sold_time time, 
    ss_item text,
    ss_sales_price float);
insert into store_sales values 
  ('2022-01-01', '09:00:00', 'Product 1', 100.0),
  ('2022-01-01', '11:00:00', 'Product 2', 500.0),
  ('2022-01-01', '15:00:00', 'Product 3', 20.0),
  ('2022-01-01', '17:00:00', 'Product 4', 1000.0),
  ('2022-01-01', '18:00:00', 'Product 5', 30.0),
  ('2022-01-02', '10:00:00', 'Product 6', 5000.0),
  ('2022-01-02', '16:00:00', 'Product 7', 5.0);

SELECT *
FROM store_sales
WHERE ss_sold_time > time '12:00:00'
QUALIFY row_number()
OVER (PARTITION BY ss_sold_date ORDER BY ss_sales_price DESC) <= 2

ss_sold_date | ss_sold_time |  ss_item  | ss_sales_price 
--------------+--------------+-----------+----------------
 2022-01-01   | 17:00:00     | Product 4 |           1000
 2022-01-01   | 18:00:00     | Product 5 |             30
 2022-01-02   | 16:00:00     | Product 7 |              5

SELECT *
FROM (
  SELECT *,
         row_number() OVER (PARTITION BY ss_sold_date ORDER BY ss_sales_price DESC) 
  FROM store_sales
  WHERE ss_sold_time > time '12:00:00'
) AS subquery
WHERE row_num <= 2;

SELECT *
FROM store_sales
QUALIFY last_value(ss_item)
OVER (PARTITION BY ss_sold_date ORDER BY ss_sold_time ASC
      ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) = ss_item;
               
ss_sold_date | ss_sold_time |  ss_item  | ss_sales_price 
--------------+--------------+-----------+----------------
 2022-01-01   | 18:00:00     | Product 5 |             30
 2022-01-02   | 16:00:00     | Product 7 |              5 

SELECT * FROM (
  SELECT *,
  last_value(ss_item)
  OVER (PARTITION BY ss_sold_date ORDER BY ss_sold_time ASC
        ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) ss_last_item
  FROM store_sales
)
WHERE ss_last_item = ss_item;