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合流KSQL中的空处理

ksql confluent apache-kafka

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Karthikeyan Rasipalay Durairaj · 技术社区 · 7 年前

你能告诉我如何处理KSQL中的空值吗。我试图处理4种可能的方法,但没有得到解决。尝试了4种方法在KSQL中用不同的值替换NULL,但给出了问题。

ksql> select PORTFOLIO_PLAN_ID from topic_stream_name; null

ksql> select COALESCE(PORTFOLIO_PLAN_ID,'N/A') from topic_stream_name; Can't find any functions with the name 'COALESCE' 
ksql> select IFNULL(PORTFOLIO_PLAN_ID,'N/A') from topic_stream_name; Function 'IFNULL' does not accept parameters of types:[BIGINT, VARCHAR(STRING)] 
ksql> select if(PORTFOLIO_PLAN_ID IS NOT NULL,PORTFOLIO_PLAN_ID,'N/A') FROM topic_stream_name; Can't find any functions with the name 'IF'

1 回复 | 直到 6 年前

1

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Robin Moffatt 7 年前

正如@cricket\u007所提到的,有一个 open ticket

您可以使用的一种解决方法是使用INSERT-INTO。它不是很优雅,当然也不像 COALESCE

# Set up some sample data, run this from bash
# For more info about kafkacat see
#    https://docs.confluent.io/current/app-development/kafkacat-usage.html
    kafkacat -b kafka-broker:9092 \
            -t topic_with_nulls \
            -P <<EOF
{"col1":1,"col2":16000,"col3":"foo"}
{"col1":2,"col2":42000}
{"col1":3,"col2":94000,"col3":"bar"}
{"col1":4,"col2":12345}
EOF

col3 :

-- Register the topic
CREATE STREAM topic_with_nulls (COL1 INT, COL2 INT, COL3 VARCHAR) \
  WITH (KAFKA_TOPIC='topic_with_nulls',VALUE_FORMAT='JSON');

-- Query the topic to show there are some null values
ksql> SET 'auto.offset.reset'='earliest';
Successfully changed local property 'auto.offset.reset' from 'null' to 'earliest'
ksql> SELECT COL1, COL2, COL3 FROM topic_with_nulls;
1 | 16000 | foo
2 | 42000 | null
3 | 94000 | bar
4 | 12345 | null

-- Create a derived stream, with just records with no NULLs in COL3
CREATE STREAM NULL_WORKAROUND AS \
  SELECT COL1, COL2, COL3 FROM topic_with_nulls WHERE COL3 IS NOT NULL;

-- Insert into the derived stream any records where COL3 *is* NULL, replacing it with a fixed string
INSERT INTO NULL_WORKAROUND \
  SELECT COL1, COL2, 'N/A' AS COL3 FROM topic_with_nulls WHERE COL3 IS NULL;

-- Confirm that the NULL substitution worked
ksql> SELECT COL1, COL2, COL3 FROM NULL_WORKAROUND;
1 | 16000 | foo
2 | 42000 | N/A
3 | 94000 | bar
4 | 12345 | N/A