Vertica 中三列（每行）的中位数 SQL

Question

我的 table 看起来像这样：

产品	长度	宽度	身高
一个	34	22	10
B	40	2	12

我想得到每个产品的最长边、第二长边和第三长边。对于最长和第三长这很容易，我就像使用 GREATEST() 和 LEAST() 一样。目前第二长的是我用子查询这样做，但这会使代码更长而且不太干净。

SELECT
product,
longest_side,
third_longest_side,
width + height + length - longest_side - third_longest_side AS second_longest_side
FROM (
      SELECT
      product,
      GREATEST(width, height, length)      AS longest_side,
      LEAST(width, height, length)         AS third_longest_side
      ...
     )

MEDIAN() 函数可以解决我的问题，但它不接受超过一列作为值。不幸的是，下面的示例不起作用。你知道任何类似的功能可以让我在没有子查询的情况下做到这一点吗？

SELECT
product,
GREATEST(width, height, length)      AS longest_side,
LEAST(width, height, length)         AS third_longest_side,
MEDIAN(width, height, length)        AS second_longest_side
...

Answer 1

您需要使用明确的逻辑。如果值都不同

select t.*,
       greatest(width, height, length) as longest_side,
       (case when width not in (least(width, height, length), greatest(width, height, length))
             then width
             when height not in (least(width, height, length), greatest(width, height, length))
             then height
             else length
        end) as middle_side
       least(width, height, length) as shortest_side

如果任何值可以是 NULL 或存在重复值，这将变得更加复杂。

Answer 2

垂直化，使用 OLAP 函数，然后再次 GROUP BY：

-- your input
WITH
indata(prd,l,w,h) AS (
          SELECT 'A',34,22,10
UNION ALL SELECT 'B',40, 2,12
)
,
-- need three key rows ....
t(t) AS (
          SELECT 'l'
UNION ALL SELECT 'w'
UNION ALL SELECT 'h'
)
,
vertical AS (
SELECT
  prd
, t
, CASE t 
    WHEN 'l' THEN l
    WHEN 'w' THEN w
    WHEN 'h' THEN h 
  END AS v
FROM indata CROSS JOIN t
)
-- test query ...
-- SELECT * FROM vertical 
-- out  prd | t | v  
-- out -----+---+----
-- out  A   | l | 34
-- out  A   | w | 22
-- out  A   | h | 10
-- out  B   | l | 40
-- out  B   | w |  2
-- out  B   | h | 12
,
olap AS (
  SELECT 
    *
  , MAX(v) OVER w AS longest_side
  , MIN(v) OVER w AS shortest_side
  , MEDIAN(v) OVER w AS medium_side
  FROM vertical
  WINDOW w AS (PARTITION BY prd)
)
-- test query ...
-- SELECT * FROM olap;
-- out  prd | t | v  | longest_side | shortest_side | medium_side 
-- out -----+---+----+--------------+---------------+-------------
-- out  B   | w |  2 |           40 |             2 |          12
-- out  B   | h | 12 |           40 |             2 |          12
-- out  B   | l | 40 |           40 |             2 |          12
-- out  A   | h | 10 |           34 |            10 |          22
-- out  A   | w | 22 |           34 |            10 |          22
-- out  A   | l | 34 |           34 |            10 |          22
SELECT
  prd
, MAX(longest_side)  AS longest_side
, MAX(shortest_side) AS shortest_side
, MAX(medium_side)   AS medium_side
FROM olap
GROUP BY 1;
-- out  prd | longest_side | shortest_side | medium_side 
-- out -----+--------------+---------------+-------------
-- out  A   |           34 |            10 |          22
-- out  B   |           40 |             2 |          12

Vertica 中三列（每行）的中位数 SQL

Median of three columns (for each row) in Vertica SQL

sql

vertica