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How to Find the Underlying Topic of a Table in ksqlDB
To know what’s the underlying topic of a table, use a DESCRIBE EXTENDED statement. Look for the first block that is printed, next to the Kafka topic label:
Name : SCORES_TABLE
Type : TABLE
Timestamp field : Not set - using <ROWTIME>
Key format : KAFKA
Value format : JSON
Kafka topic : scores_topic (partitions: 10, replication: 3)
Statement : CREATE TABLE SCORES_TABLE (STUDENT_ID BIGINT PRIMARY KEY, NAME STRING, SCORE DOUBLE) WITH (KAFKA_TOPIC='scores_topic', KEY_FORMAT='KAFKA', PARTITIONS=10, VALUE_FORMAT='JSON');
In that case, the underlying Kafka topic is called scores_topic.
Regardless of whether the table is materialized or not, there will always be an underlying topic.
Materialized tables will have an underlying topic that was created as a result of the materialization.
If you need to search
for the root topic, you can find find the Statement label within the DESCRIBE EXTENDED statement output, and look at the stream or table that is used as a source. You can then describe
t
he stream or table you identified to find out more. Repeat these steps until you find the topic that you are looking for.
This is especially important when creating tombstone tables to delete rows from a table.
Alternatively, you can also know about the underlying topics when listing all the tables in the cluster:
LIST TABLES;
Table Name | Kafka Topic | Key Format | Value Format | Windowed
-----------------------------------------------------------------------------------------
ALICE_SCORE | ALICE_SCORE | KAFKA | JSON | false
SCORES_EMPTY_TABLE | scores_topic | KAFKA | JSON | false
SCORES_EMPTY_TABLE_MAT | SCORES_EMPTY_TABLE_MAT | KAFKA | JSON | false
SCORES_SOURCE_TABLE | scores_topics | KAFKA | JSON | false
SCORES_TABLE_TOMBSTONES | scores_topic | KAFKA | KAFKA | false
-----------------------------------------------------------------------------------------
Note the Kafka Topic column.