创建KSQL流:如何从复杂的json中提取值

Question

我正在尝试在Apache/KAFKA KSQL中创建一个流主题包含(有点复杂的JSON)

{
  "agreement_id": "dd8afdbe-59cf-4272-b640-b14a24d8234c",
  "created_at": "2018-02-17 16:00:00.000Z",
  "id": "6db276a8-2efe-4495-9908-4d3fc4cc16fa",
  "event_type": "data",
  "total_charged_amount": {
    "tax_free_amount": null,
    "tax_amounts": [],
    "tax_included_amount": {
      "amount": 0.0241,
      "currency": "EUR"
    }
  }
  "used_service_units": [
    {
      "amount": 2412739,
      "currency": null,
      "unit_of_measure": "bytes"
    }
  ]
}

现在创建一个流很容易就像event_type和created_at这样简单的东西.那会是这样的

CREATE STREAM tstream (event_type varchar, created_at varchar) WITH (kafka_topic='usage_events', value_format='json');

但现在我需要访问used_service_units ....我想在上面的JSON中提取"金额"

我该怎么做？

CREATE STREAM usage (event_type varchar,create_at varchar, used_service_units[0].amount int) WITH (kafka_topic='usage_events', value_format='json');

结果是

line 1:78: mismatched input '[' expecting {'ADD', 'APPROXIMATE', ...

如果我改为创建一个像这样的流

CREATE STREAM usage (event_type varchar,create_at varchar, used_service_units varchar) WITH (kafka_topic='usage_events', value_format='json');

然后像这样在流上做一个SQL SELECT

SELECT EXTRACTJSONFIELD(used_service_units,'$.amount') FROM usage;
SELECT EXTRACTJSONFIELD(used_service_units[0],'$.amount') FROM usage;
SELECT EXTRACTJSONFIELD(used_service_units,'$[0].amount') FROM usage;

这些替代品都不起作用......

这个给了我

SELECT EXTRACTJSONFIELD(used_service_units[0],'$.amount') FROM usage;'

Code generation failed for SelectValueMapper

Answer 1

似乎这个问题的一个解决方案是使列数据类型成为一个数组即

CREATE STREAM usage (event_type varchar,created_at varchar, total_charged_amount varchar, used_service_units array<varchar> ) WITH (kafka_topic='usage_events', value_format='json');

现在我能够做到以下几点:

SELECT EXTRACTJSONFIELD(used_service_units[0],'$.amount') FROM usage