創建 KSQL 流：如何從復雜的 json 中提取值

Question

我正在嘗試在 Apache/KAFKA KSQL 中創建一個流主題包含（有點復雜的 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"
    }
  ]
}

現在創建流很容易，只需簡單的東西，比如 event_type 和 created_at。 就是這樣

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

但是現在我需要訪問 used_service_units .... 我想在上面的 JSON 中提取“數量”

我該怎么做？

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

結果是

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

如果我改為像這樣創建一個流

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

然后像這樣在流上執行 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;

這些替代方案都不起作用......

這個給了我

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

Code generation failed for SelectValueMapper

Answer 1

似乎這個問題的一個解決方案是使列數據類型成為一個數組，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');

現在我可以執行以下操作：

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