Before you can drop a stream or table that’s populated by a query in KSQL, you have to terminate any queries upon which the object is dependent. Here’s a bit of jq & xargs magic to terminate all queries that are currently running

 curl -s -X "POST" "http://localhost:8088/ksql" \
         -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
         -d '{"ksql": "SHOW QUERIES;"}' | \
  jq '.[].queries[].id' | \
  xargs -Ifoo curl -X "POST" "http://localhost:8088/ksql" \
           -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
           -d '{"ksql": "TERMINATE 'foo';"}'

To drop all streams:

curl -s -X "POST" "http://localhost:8088/ksql" \
           -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
           -d '{"ksql": "SHOW STREAMS;"}' | \
    jq '.[].streams[].name' | \
    xargs -Ifoo curl -X "POST" "http://localhost:8088/ksql" \
             -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
             -d '{"ksql": "DROP STREAM 'foo';"}'

To drop all tables:

curl -s -X "POST" "http://localhost:8088/ksql" \
             -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
             -d '{"ksql": "SHOW TABLES;"}' | \
      jq '.[].tables[].name' | \
      xargs -Ifoo curl -X "POST" "http://localhost:8088/ksql" \
               -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
               -d '{"ksql": "DROP TABLE 'foo';"}'

For more notes on the KSQL REST API see the docs and this cheatsheet.

Courtesy of Evelyn Munkel via the 💬 Confluent Community Slack group, a way to target just a particular stream:

echo Terminating the write query for the FOO stream
curl -s -X "POST" ${ksql.url} \
    -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
    -d '{"ksql": "DESCRIBE FOO;"}' \ |
    jq '.[].sourceDescription.writeQueries[].id' | \
 xargs -Iq1 curl -X "POST" ${ksql.url} \
          -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
          -d '{"ksql": "TERMINATE 'q1';"}' | jq

echo Terminating the read query for the FOO stream
curl -s -X "POST" ${ksql.url} \
    -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
    -d '{"ksql": "DESCRIBE FOO;"}' \ |
    jq '.[].sourceDescription.readQueries[].id' | \
 xargs -Iq3 curl -X "POST" ${ksql.url} \
          -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
          -d '{"ksql": "TERMINATE 'q3';"}' | jq

echo Dropping the FOO stream
curl -X "POST" ${ksql.url} \
            -H "Content-Type: application/vnd.ksql.v1+json; charset=utf-8" \
            -d '{"ksql": "DROP TABLE FOO;"}' | jq