无法在 Presto Athena 中将 varchar 转换为数组 [英] Unable to convert varchar to array in Presto Athena

问题描述

我的数据是 varchar 格式.我想拆分这个数组的两个元素，以便我可以从 json 中提取一个键值.

My data is in varchar format. I want to split both the elements of this array so that I can then extract a key value from the json.

Data format:

[
  {
    "skuId": "5bc87ae20d298a283c297ca1",
    "unitPrice": 0,
    "id": "5bc87ae20d298a283c297ca1",
    "quantity": "1"
  },

{
    "skuId": "182784738484wefhdchs4848",
    "unitPrice": 50,
    "id": "5bc87ae20d298a283c297ca1",
    "quantity": "4"
  },
]

例如我想从上列中提取 skuid.所以我提取后的数据应该是这样的:

For e.g. I want to extract skuid from the above column. So my data after extraction should look like:

1 5bc87ae20d298a283c297ca1
2 182784738484wefhdchs4848

强制转换为数组不起作用例如 select cast(col as array) 给出以下错误:未知类型:数组

Cast to array doesn't work e.g select cast(col as array) gives the following error: Unknown type: array

所以我无法取消嵌套数组.

So I am not able to unnest the array.

我如何在 Athena 中解决这个问题?

How do I do solve this problem in Athena?

推荐答案

你可以组合使用 将值解析为 JSON，将其转换为结构化 SQL 类型(数组/地图/行)，以及 UNNEST WITH ORDINALITY 从数组中提取元素作为单独的行.请注意，这仅在 JSON 有效负载中的数组元素没有尾随逗号时才有效.您的示例有一个，但已从下面的示例中删除.

You can use a combination of parsing the value as JSON, casting it to a structured SQL type (array/map/row), and UNNEST WITH ORDINALITY to extract the elements from the array as separate rows. Note that this only works if the array elements in the JSON payload don't have a trailing commas. Your example has one but it is removed from the example below.

WITH data(value) AS (VALUES
 '[
    {
      "skuId": "5bc87ae20d298a283c297ca1",
      "unitPrice": 0,
      "id": "5bc87ae20d298a283c297ca1",
      "quantity": "1"
    },
    {
      "skuId": "182784738484wefhdchs4848",
      "unitPrice": 50,
      "id": "5bc87ae20d298a283c297ca1",
      "quantity": "4"
    }
  ]'
),
parsed(entries) AS (
  SELECT cast(json_parse(value) AS array(row(skuId varchar)))
  FROM data
)
SELECT ordinal, skuId
FROM parsed, UNNEST(entries) WITH ORDINALITY t(skuId, ordinal)

产生:

 ordinal |          skuId
---------+--------------------------
       1 | 5bc87ae20d298a283c297ca1
       2 | 182784738484wefhdchs4848
(2 rows)

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