如何将函数应用于数组列的每个元素？

Question

我有一个数据集，其中有一列包含对象数组，如下所示：

ID   TAGS
1    {"tags": [{"tag": "a"}, {"tag": "b"}]}
2    {"tags": [{"tag": "c"}, {"tag": "d"}]}

我想提取tag数组每个元素的字段，所以最终结果是：

ID   TAGS
1    ["a","b"]
2    ["c","d"]

假设如下表t1：

CREATE OR REPLACE TEMPORARY TABLE t1 AS (
      select 1 as ID , PARSE_JSON('{"tags": [{"tag":"a"}, {"tag":"b"}]}') AS PAYLOAD
    UNION ALL
    select 2, PARSE_JSON('{"tags": [{"tag":"c"}, {"tag":"d"}]}')

);

Answer 1

纯 SQL 方法是将LATERAL FLATTEN和ARRAY_AGG结合起来，如下所示：

with t2 as (
    select ID, t2.value:tag as tag
    from t1, LATERAL FLATTEN(input => payload:tags) t2
)
select t2.id, ARRAY_AGG(t2.tag) as tags from t2
group by ID 
order by ID ASC;

t2 本身将变成：

ID  TAG
1   "a"
1   "b"
2   "c"
2   "d"

之后就GROUP BY ID变成：

ID  TAGS
1   [    "a",    "b"  ]
2   [    "c",    "d"  ]