json - Presto unnest json 映射

Question

关注这些帖子:How to cross join unnest a JSON array in Presto和 Presto unnest json我无法将我的 JSON 映射到所需的表中。

当我运行这个 presto 时:

SELECT
    *
FROM UNNEST(
        CAST(
            JSON_EXTRACT('{"1":{"a":10,"b":11},"2":{"a":20,"b":21}}', '$.1') AS ARRAY(
                VARCHAR
                -- ROW(VARCHAR, BIGINT)
                -- MAP(VARCHAR, MAP(VARCHAR, BIGINT))
            )
        )
    ) AS x(n)

我明白了:

(INVALID_CAST_ARGUMENT) Cannot cast to array(varchar). Expected a json array, but got {
{"a":10,"b":11} ... 

但我理想的预期答案是:

  a | b
 ---+---
 10 | 11
 20 | 21

如何UNNEST Map 而不是数组？

Answer 1

您的目标的正确 json 路径是 $.* 但通配符 are not supported by presto ，因此您可以将 json 转换为 map of maps 并使用它:

SELECT maps['a'] a, maps['b'] b
FROM (UNNEST(map_values(
        CAST(JSON '{"1":{"a":10,"b":11},"2":{"a":20,"b":21}}' AS MAP(VARCHAR , MAP(VARCHAR, INTEGER)))))) as tmp(maps);