Snowflake cloud data platform 如何将函数应用于数组列的每个元素？

我有一个数据集，其中包含一列对象，如下所示：

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

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;

我想提取数组中每个元素的

标记

字段，因此最终结果是：

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

假设下表

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"}]}')

);

---

一种可能的解决方案是创建javascript函数，并使用将函数应用于数组的每个元素：

create or replace function extract_tags(a array)
  returns array
  language javascript
  strict
  as '

  return A.map(function(d) {return d.tag});
  ';

SELECT ID, EXTRACT_TAGS(PAYLOAD:tags) AS tags from t1;

这将产生预期的结果：

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

---

纯SQL方法是组合如下：

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

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本身将成为：

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

在

按ID分组后，它变成：

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

为了使事情更灵活，您还可以返回指定的键（而不是硬编码
标记
）。签名如下：
extract（数组，k字符串）
，您只需返回
d[k]
，而不是
d.tag
。