尽管有参数，KSQLDB coalesce 总是返回 null

Question

我有以下 ksql 查询：

SELECT 
  event->acceptedevent->id as id1, 
  event->refundedevent->id as id2, 
  coalesce(event->acceptedevent->id, event->refundedevent->id) as coalesce_col 
FROM events 
EMIT CHANGES;

根据文档，(https://docs.ksqldb.io/en/latest/developer-guide/ksqldb-reference/scalar-functions/#coalesce) COALESCE 返回第一个非空参数。

查询返回以下内容：

+-----------------------------------------------+-----------------------------------------------+-----------------------------------------------+
|ID1                                            |ID2                                            |COALESCE_COL                                   |
+-----------------------------------------------+-----------------------------------------------+-----------------------------------------------+
|1                                              |null                                           |null                                           |
|2                                              |null                                           |null                                           |
|3                                              |null                                           |null                                           |

我期待，因为 ID1 显然不是 null，作为调用的第一个参数，COALESCE 将返回与 ID1 相同的值，但它返回 null。我错过了什么？

我正在使用 confluentinc/cp-ksqldb-server:6.1.1 并使用 avro 作为值 serde。

EventMessage.avsc：

{
  "type": "record",
  "name": "EventMessage",
  "namespace": "com.example.poc.processor2.avro",
  "fields": [
    {
      "name": "event",
      "type": [
        "com.example.poc.processor2.avro.AcceptedEvent",
        "com.example.poc.processor2.avro.RefundedEvent"
      ]
    }
  ]
}

Answer 1

可能是数据反序列化方式或 COALESCE 函数的错误。

• 你运行的是什么 KSQL 版本
• 您的数据在主题中是如何序列化的？

我尝试了 JSON 格式，它成功了。

ksql> describe events;

Name                 : EVENTS
 Field | Type                                                                       
------------------------------------------------------------------------------------
 EVENT | STRUCT<ACCEPTEDEVENT STRUCT<ID INTEGER>, REFUNDEDEVENT STRUCT<ID INTEGER>> 
------------------------------------------------------------------------------------

ksql> print 'events' from BEGINNING;
Key format: ¯\_(ツ)_/¯ - no data processed
Value format: JSON or KAFKA_STRING
rowtime: 2021/03/24 13:57:27.403 Z, key: <null>, value: {"event":{"acceptedevent":{"id":1}, "refundedevent":{}}}, partition: 


ksql> select event->acceptedevent->id, event->refundedevent->id, coalesce(event->acceptedevent->id, event->refundedevent->id) from events emit changes;
+----------------------------------------------------------+----------------------------------------------------------+----------------------------------------------------------+
|ID                                                        |ID_1                                                      |KSQL_COL_0                                                |
+----------------------------------------------------------+----------------------------------------------------------+----------------------------------------------------------+
|1                                                         |null                                                      |1                                                         |