如何在presto db中扩展字典列表

Question

我在 prestodb 中有一列是字典列表：

[{"id": 45238, "kind": "product", "name": "Ball", "category": "toy"}, {"id": 117852, "kind": "service", "name": "courier", "category": "transport"}]

有没有办法扩展此列以获得如下内容：

id     kind      name      category
4528   product   Ball      toy
117852 service   courier   transport

有时密钥可能与上面的示例不同，也可能比上面的 4 个密钥更多

我正在尝试：

with cte as ( select cast(divs as json) as json_field from table)
select m['id'] id, 
    m['kind'] kind,
    m['name'] name,
    m['category'] category
from cte
cross join unnest(cast(json_field as array(map(varchar, json)))) as t(m)

错误：

INVALID_CAST_ARGUMENT: Cannot cast to array(map(varchar, json)). Expected a json array, but got [{"id": 36112, "kind"....

Answer 1

假设您的数据包含 json - 您可以将其转换为从 varchar 到 json (array(map(varchar, json))) 的映射数组，然后使用 unnest 来展平数组:

WITH dataset (json_str) AS (
    VALUES (json '[{"id": 45238, "kind": "product", "name": "Ball", "category": "toy"}, {"id": 117852, "kind": "service", "name": "courier", "category": "transport"}]')
) 

select m['id'] id, 
    m['kind'] kind,
    m['name'] name,
    m['category'] category
from dataset
cross join unnest(cast(json_str as array(map(varchar, json)))) as t(m)

id	kind	name	category
45238	product	Ball	toy
117852	service	courier	transport

UPD

如果原始列类型是 varchar - 使用 json_parse 将其转换为 json。

如何在presto db中扩展字典列表

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