从 BigQuery 中的 JSON ARRAY 中提取值答案

【问题标题】：Extract value from JSON ARRAY in BigQuery从 BigQuery 中的 JSON ARRAY 中提取值
【发布时间】：2021-08-06 22:07:36
【问题描述】：

我正在尝试从 JSON ARRAY 中提取值，如下所示

  with `project.dataset.table` as (
  select '{"fruit":[{"apples":"5","oranges":"10","pear":"20"},
                    {"apples":"5","oranges":"4"},
                    {"apples":"5","oranges":"9","pear":"40"}]}' as json union all
  select '{"fruit":[{"lettuce":"7","kale": "8"}]}' 
)

select json, if(regexp_contains(json, '"apples":"5"'), (SELECT 
ARRAY_AGG(json_extract_scalar(arr, '$.oranges') ignore nulls)
from 
UNNEST(json_extract_ARRAY(json, '$.fruit')) as arr ), null) as oranges,
if(regexp_contains(json, '"apples":"5"'), (SELECT 
ARRAY_AGG(json_extract_scalar(arr, '$.pear') ignore nulls)
from 
UNNEST(json_extract_ARRAY(json, '$.fruit')) as arr ), null) as pear,
from `project.dataset.table`

输出如下

我期待像这样的输出

json	oranges	pear
{"fruit":[{"apples":"5","oranges":"10","pear":"20"},{"apples":"5","oranges":"4"},{"apples":"5","oranges":"9","pear":"40"}]}	10	20
	4	null
	9	40
{"fruit":[{"lettuce":"7","kale": "8"}]}.	null	null

【问题讨论】：

标签： json google-cloud-platform google-bigquery

【解决方案1】：

考虑下面的方法，更明确地对齐各个条目

select json, 
  array(
    select 
      if(
        json_extract_scalar(val, '$.apples') = '5',
        struct(
          json_extract_scalar(val, '$.oranges') as oranges,
          json_extract_scalar(val, '$.pear') as pear
        ),
        struct(null, null)
      )
    from t.arr val
  ) fruits
from `project.dataset.table`, 
unnest([struct(json_extract_array(json, '$.fruit') as arr)]) t

它不那么冗长，并且输出水果作为重复记录而不是两个数组
如果应用于问题输出中的样本数据是

如果您确实需要将输出保留为单独的列 - 请在下面使用

select json, 
  array(
    select 
      if(
        json_extract_scalar(val, '$.apples') = '5',
        ifnull(json_extract_scalar(val, '$.oranges'), '0'),
        '0'
      )
    from t.arr val
  ) as oranges,
  array(
    select 
      if(
        json_extract_scalar(val, '$.apples') = '5',
        ifnull(json_extract_scalar(val, '$.pear'), '0'),
        '0'
      )
    from t.arr val
  ) as pear
from `project.dataset.table`, 
unnest([struct(json_extract_array(json, '$.fruit') as arr)]) t

有输出

【讨论】：

感谢您的帮助 :) 它对我有用！

【解决方案2】：

使用array_agg时

如果最终查询结果中的数组包含 NULL 元素。

您可以尝试像这样使用字符串'null'：

with `project.dataset.table` as (
  select '{"fruit":[{"apples":"5","oranges":"10","pear":"20"},{"apples":"5","oranges":"4"},{"apples":"5","oranges":"9","pear":"40"}]}' as json union all
  select '{"fruit":[{"lettuce":"7","kale": "8"}]}' 
)
select 
  json,
  if( regexp_contains(json, '"apples":"5"'),
    (SELECT ARRAY_AGG(ifnull(json_extract_scalar(arr, '$.oranges'), 'null')) from UNNEST(json_extract_ARRAY(json, '$.fruit')) as arr ),
    ['null']
  ) as oranges,
  if( regexp_contains(json, '"apples":"5"'),
    (SELECT ARRAY_AGG(ifnull(json_extract_scalar(arr, '$.pear'), 'null')) from UNNEST(json_extract_ARRAY(json, '$.fruit')) as arr ),
    ['null']
  ) as pear,
from `project.dataset.table`

【讨论】：

谢谢你的回答:)