BigQuery 标准 SQL:如何按 ARRAY 字段分组 [英] BigQuery standard SQL: how to group by an ARRAY field

问题描述

我的表有两列，id 和 a.id 列包含一个数字，a 列包含一个字符串数组.我想计算给定数组的唯一 id 数，数组之间的相等性被定义为每个索引的大小相同，字符串相同".

My table has two columns, id and a. Column id contains a number, column a contains an array of strings. I want to count the number of unique id for a given array, equality between arrays being defined as "same size, same string for each index".

当使用 GROUP BY a 时，我得到 不允许按 ARRAY 类型的表达式分组.我可以使用类似 GROUP BY ARRAY_TO_STRING(a, ",") 的东西，但是两个数组 ["a,b"] 和 ["a","b"] 组合在一起，我失去了数组的真实"值(所以如果我想稍后在另一个查询中使用它，我必须拆分字符串).

When using GROUP BY a, I get Grouping by expressions of type ARRAY is not allowed. I can use something like GROUP BY ARRAY_TO_STRING(a, ","), but then the two arrays ["a,b"] and ["a","b"] are grouped together, and I lose the "real" value of my array (so if I want to use it later in another query, I have to split the string).

这个字段数组中的值来自用户，所以我不能假设某些字符根本不会存在(并将其用作分隔符).

The values in this field array come from the user, so I can't assume that some character is simply never going to be there (and use it as a separator).

推荐答案

代替 GROUP BY ARRAY_TO_STRING(a, ",") 使用 GROUP BY TO_JSON_STRING(a)

因此您的查询将如下所示

so your query will look like below

#standardsql
SELECT 
  TO_JSON_STRING(a) arr,
  COUNT(DISTINCT id) cnt
FROM `project.dataset.table`
GROUP BY arr

您可以使用如下虚拟数据进行测试

You can test it with dummy data like below

#standardsql
WITH `project.dataset.table` AS (
  SELECT 1 id, ["a,b", "c"] a UNION ALL
  SELECT 1, ["a","b,c"]
)
SELECT 
  TO_JSON_STRING(a) arr,
  COUNT(DISTINCT id) cnt
FROM `project.dataset.table`
GROUP BY arr  

结果为

Row     arr             cnt  
1       ["a,b","c"]     1    
2       ["a","b,c"]     1    

根据@Ted 的评论更新

Update based on @Ted's comment

#standardsql
SELECT 
  ANY_VALUE(a) a,
  COUNT(DISTINCT id) cnt
FROM `project.dataset.table`
GROUP BY TO_JSON_STRING(a)

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