sql　窗口查询

WITH Produce AS
 (SELECT 'kale' as item, 23 as purchases, 'vegetable' as category
  UNION ALL SELECT 'orange', 2, 'fruit'
  UNION ALL SELECT 'cabbage', 9, 'vegetable'
  UNION ALL SELECT 'apple', 8, 'fruit'
  UNION ALL SELECT 'leek', 2, 'vegetable'
  UNION ALL SELECT 'lettuce', 10, 'vegetable')
 
 
SELECT item, purchases, category, LAST_VALUE(item)
  OVER (  PARTITION BY category
  ORDER BY purchases
  ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING) AS most_popular
FROM Produce

等价与下面

WITH Produce AS
 (SELECT 'kale' as item, 23 as purchases, 'vegetable' as category
  UNION ALL SELECT 'orange', 2, 'fruit'
  UNION ALL SELECT 'cabbage', 9, 'vegetable'
  UNION ALL SELECT 'apple', 8, 'fruit'
  UNION ALL SELECT 'leek', 2, 'vegetable'
  UNION ALL SELECT 'lettuce', 10, 'vegetable')
 
 
SELECT item, purchases, category, LAST_VALUE(item)
  OVER (item_window) AS most_popular
FROM Produce
WINDOW item_window AS (
  PARTITION BY category
  ORDER BY purchases
  ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)