在presto中将行扩展为列

Question

有没有办法在presto中有效地将行扩展为列？

我尝试用“where team=1”和“where team=2”分别过滤原始数据集，首先相应地获得dataset1和DataSet2，然后在income_level上连接这两个数据集。然而，当income_level有太多不同的值时，这是不方便的。有没有什么高效的方法可以得到我想要的结果？

Answer 1

Prestodb提供了一个map_agg函数，可以帮助将长数据转换为您需要的宽格式。不幸的是，似乎没有一种方法可以动态地创建列名，但是这种方法应该比加入每个团队更有效（并且更少键入：））。

WITH raw_data AS (
  SELECT 1 AS team, 'a' AS income_level, 1 AS time, 11 AS ord
  UNION
  SELECT 1 AS team, 'b' AS income_level, 2 AS time, 12 AS ord
  UNION
  SELECT 1 AS team, 'c' AS income_level, 3 AS time, 13 AS ord
  UNION
  SELECT 2 AS team, 'a' AS income_level, 4 AS time, 14 AS ord
  UNION
  SELECT 2 AS team, 'b' AS income_level, 5 AS time, 15 AS ord
  UNION
  SELECT 2 AS team, 'c' AS income_level, 6 AS time, 16 AS ord
  UNION
  SELECT 3 AS team, 'a' AS income_level, 7 AS time, 17 AS ord
  UNION
  SELECT 3 AS team, 'b' AS income_level, 8 AS time, 18 AS ord
  UNION
  SELECT 3 AS team, 'c' AS income_level, 9 AS time, 19 AS ord
)

SELECT
  income_level,
  team_time[1] AS time_1,
  team_ord[1] AS ord_1,
  team_time[2] AS time_2,
  team_ord[2] AS ord_2,
  team_time[3] AS time_3,
  team_ord[3] AS ord_3
FROM (
  SELECT
    income_level,
    map_agg(team, time) AS team_time,
    map_agg(team, ord) AS team_ord
  FROM raw_data
  GROUP BY income_level
);

输出：

| income_level | time_1 | ord_1 | time_2 | ord_2 | time_3 | ord_3 |
|--------------|--------|-------|--------|-------|--------|-------|
| a            | 1      | 11    | 4      | 14    | 7      | 17    |
| b            | 2      | 12    | 5      | 15    | 8      | 18    |
| c            | 3      | 13    | 6      | 16    | 9      | 19    |

这个网站提供了另一个例子，说明如何做到这一点。