sql - 在 Presto 中从 JSON 数组中提取值

Question

我有一列包含 JSON 数组，如下所示:

{data=[{"name":"col1","min":0,"max":32,"avg":29},
{"name":"col2","min":1,"max":35,"avg":21},
{"name":"col3","min":4,"max":56,"avg":34}]}

我正在尝试解析数组并根据条件提取特定值。例如 "min" 的值哪里 "name"="col1" : 0 "avg" 的值哪里 "name"="col3" : 34
有没有人有解决方案？

Answer 1

您的 JSON 无效。应该是 {"data":[不是 {data = [如果 JSON 有效(您可以在子查询中轻松修复它)，提取数据，将其转换为数组(行)并使用 CASE 表达式获取值。我在这里添加了 max() 聚合以删除 NULL 记录并在单行中获取所有必需的值，您可以改用过滤器(例如 where x.name = 'col1' )，具体取决于您的需要:

with mydata as (
select '{"data":[{"name":"col1","min":0,"max":32,"avg":29},
{"name":"col2","min":1,"max":35,"avg":21},
{"name":"col3","min":4,"max":56,"avg":34}]}' json
)

select max(case when x.name = 'col1' then x.min end) min_col1,
       max(case when x.name = 'col3' then x.avg end) avg_col3
from mydata
CROSS JOIN
    UNNEST(
            CAST(
                JSON_EXTRACT(json,'$.data')
                    as ARRAY(ROW(name VARCHAR, min INTEGER, max INTEGER, avg INTEGER))
                 )
          ) as x(name, min, max, avg) --column aliases

结果:

min_col1    avg_col3
0           34