Example of how KSQL protects against dropping tables and streams which are in use.

safe-drop-example.sh

ksql> show queries;

 Query ID                      | Kafka Topic              | Query String                                                                                                              
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 CSAS_PAGEVIEWS_ENRICHED       | PAGEVIEWS_ENRICHED       | CREATE STREAM pageviews_enriched AS SELECT users_original.userid AS userid, pageid, regionid, gender FROM pageviews_original LEFT JOIN users_original ON pageviews_original.userid = users_original.userid;
 CSAS_PAGEVIEWS_FEMALE         | PAGEVIEWS_FEMALE         | CREATE STREAM pageviews_female AS SELECT * FROM pageviews_enriched WHERE gender = 'FEMALE';                               
 CSAS_PAGEVIEWS_FEMALE_LIKE_89 | pageviews_enriched_r8_r9 | CREATE STREAM pageviews_female_like_89 WITH (kafka_topic='pageviews_enriched_r8_r9', value_format='DELIMITED') AS SELECT * FROM pageviews_female WHERE regionid LIKE '%_8' OR regionid LIKE '%_9';
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For detailed information on a Query run: EXPLAIN <Query ID>;
ksql> drop stream PAGEVIEWS_ENRICHED;
Cannot drop the data source. The following queries read from this source: [CSAS_PAGEVIEWS_FEMALE] and the following queries write into this source: [CSAS_PAGEVIEWS_ENRICHED]. You need to terminate them before dropping this source.
ksql>