Google Cloud - BigQuery - 在结构中转置 2 个字符串列答案

【问题标题】：Google Cloud - BigQuery - Transposing 2 String Columns within a StructGoogle Cloud - BigQuery - 在结构中转置 2 个字符串列
【发布时间】：2021-06-01 15:56:38
【问题描述】：

大家早上好，

BigQuery 新手，我在过去使用过的其他 BI 语言中发现了一些非常直观的东西，即转置键和值，以便键成为列名，值成为与列关联的值.

我在网上查看了一些示例，当我处理它们时，我遇到了许多我无法解决的错误，因为我没有足够的经验。

对于那些不可避免地质疑我为什么要这样做的人，这是我有义务满足的业务要求，但是如果您对解决此问题的更好方法有任何想法，我非常乐意接受此建议并欣赏它。

**The Json:**

[
  {
    "resultsMap": {
      "map": {
        "item": [
          {
            "value": "2021-03-02-12.16.28.012279",
            "key": "TIMESTAMP"
          },
          {
            "value": "1",
            "key": "CONTROL_KEY"
          },
          {
            "value": "123465789",
            "key": "LOGGING_KEY"
          }
        ],
        "key": "5049"
      }
    }
  }
]

我有什么

resultsMap.map.key	resultsMap.map.item.value	resultsMap.map.item.key
5049	TIMESTAMP	2021-03-02-12.16.28.012279
	CONTROL_KEY	1
	LOGGING_KEY	123456789

我想要什么

resultsMap.map.key	TIMESTAMP	CONTROL_KEY	LOGGING_KEY
5049	2021-03-02-12.16.28.012279	1	123456789

非常感谢您的帮助。

问候，斯科特

【问题讨论】：

标签： arrays struct google-bigquery

【解决方案1】：

对于这种情况，我们必须手动从数组中选择：

with mytable as (
  select struct( struct(5049 as key, [struct("2021-03-02-12.16.28.012279" as value, "TIMESTAMP" as key), struct("1" as value, "CONTROL_KEY" as key), struct("123465789" as value, "LOGGING_KEY" as key)] as item) as map) as resultsMap
)
select
  resultsMap.map.key,
  (select value from unnest(resultsMap.map.item) where key = 'TIMESTAMP') as TIMESTAMP,
  (select value from unnest(resultsMap.map.item) where key = 'CONTROL_KEY') as CONTROL_KEY,
  (select value from unnest(resultsMap.map.item) where key = 'LOGGING_KEY') as LOGGING_KEY
from mytable

【讨论】：

【解决方案2】：

也考虑下面（假设所有要提取的键都存在）：

select resultsMap.map.key,
  kv[offset(0)] as TIMESTAMP, 
  kv[offset(1)] as CONTROL_KEY, 
  kv[offset(2)] as LOGGING_KEY, 
from `project.dataset.table` t, 
unnest([(
  select as struct array_agg(value 
    order by case key 
      when 'TIMESTAMP' then 0 
      when 'CONTROL_KEY' then 1 
      when 'LOGGING_KEY' then 2 
    end) as kv 
  from t.resultsMap.map.item 
)])

还有进一步重构的版本：

select resultsMap.map.key,
  kv[offset(2)] as TIMESTAMP, 
  kv[offset(0)] as CONTROL_KEY, 
  kv[offset(1)] as LOGGING_KEY, 
from `project.dataset.table` t,
unnest([(
  select as struct array_agg(value 
    order by range_bucket(key, ['CONTROL_KEY','LOGGING_KEY','TIMESTAMP'])
  ) as kv 
  from t.resultsMap.map.item 
)])

如果应用于您问题中的样本数据 - 输出是

【讨论】：