如何在 BigQuery 中将数据分组为结构？

Question

我有以下数据：

player_id level talent_id
1         1     a
1         2     b
1         3     c
2         1     d
2         2     e

并希望按player_id分组并将行作为结构，将level值作为结构字段名称：

player_id data
1         {_1 = a, _2 = b, _3 = c}
2         {_1 = d, _2 = e, _3 = null}

级别列始终来自 {1, 2, 3} 集合，但某些级别可能会丢失（空）

到目前为止，我得到的是按player_id 进行聚合并附加结果数组：

talents as (
  select
    p.player_id,
    array_agg(struct(p.level, p.talent_id)) as talents
  from source.player_talent p
  group by player_id
),

player_id data
1         [{1, a}, {2, b}, {3, c}]
2         {{1, d}, {2, e}]

现在我需要将此数组映射到具有固定属性名称的结构_1，，_2_3

Answer 1

这将返回预期结果：

WITH Players AS (
  SELECT 1 AS player_id, 1 AS level, 'a' AS talent_id UNION ALL
  SELECT 1, 2, 'b' UNION ALL
  SELECT 1, 3, 'c' UNION ALL
  SELECT 2, 1, 'd' UNION ALL
  SELECT 2, 2, 'e'
)
SELECT
  player_id,
  STRUCT(
    MAX(IF(level = 1, talent_id, NULL)) AS _1,
    MAX(IF(level = 2, talent_id, NULL)) AS _2,
    MAX(IF(level = 3, talent_id, NULL)) AS _3) AS data
FROM Players
GROUP BY player_id

这里的技术称为旋转（将行转换为列）。