PRINT statement in ksqlDB for Confluent Platform¶
Synopsis¶
PRINT topicName [FROM BEGINNING] [INTERVAL | SAMPLE interval] [LIMIT limit]
Description¶
Print the contents of Kafka topics to the ksqlDB CLI.
The topicName is case sensitive. Quote the name if it contains invalid characters. See Valid Identifiers for more information.
The PRINT statement supports the following properties:
| Property | Description |
|---|---|
| FROM BEGINNING | Print starting with the first message in the topic. If not specified, PRINT starts with the most recent message. |
| INTERVAL interval | Print every interval th message. The default is 1,
meaning that every message is printed. |
| LIMIT limit | Stop printing after limit messages. The default value
is unlimited, requiring Ctrl+C to terminate the query. |
Example¶
The following statement shows how to print all of the records in a topic
named rider-locations, created by:
CREATE STREAM riderLocations (profileId VARCHAR, latitude DOUBLE, longitude DOUBLE)
WITH (kafka_topic='rider-locations', value_format='json', partitions=1);
Note, the topic name has been quoted as it contains the invalid dash character.
PRINT 'rider-locations' FROM BEGINNING;
ksqlDB attempts to determine the format of the data in the topic and outputs what it thinks are the key and value formats at the top of the output.
Note
Attempting to determine a data format from only the serialized bytes is not
an exact science! For example, it is not possible to distinguish between
serialized BIGINT and DOUBLE values, because they both occupy eight
bytes. Short strings can also be mistaken for serialized numbers. Where it
appears different records are using different formats ksqlDB will state the
format is MIXED.
The output should resemble:
Key format: JSON or KAFKA_STRING
Value format: JSON or KAFKA_STRING
rowtime: 2022/03/18 15:53:22.989 Z, key: 18, value: {"ordertime":1497014222380,"orderid":18,"itemid":"Item_184","address":{"city":"Mountain View","state":"CA","zipcode":94041}}, partition: 0
rowtime: 2022/03/18 15:53:27.192 Z, key: 18, value: {"ordertime":1497014222380,"orderid":18,"itemid":"Item_184","address":{"city":"Mountain View","state":"CA","zipcode":94041}}, partition: 0
^CTopic printing ceased
The key format for this topic is KAFKA_STRING. However, the
PRINT command does not know this and has attempted to determine the
format of the key by inspecting the data. It has determined that the
format may be KAFKA_STRING, but it could also be JSON.
The value format for this topic is JSON. However, the PRINT
command has also determined it could be KAFKA_STRING. This is
because JSON is serialized as text. Hence you could choose to
deserialize this value data as a KAFKA_STRING if you wanted to.
However, JSON is likely the better option.