Probably the most common question in the Confluent Community Slack group’s #ksql channel is:
Why isn’t my KSQL query returning data?
That is, you’ve run a
CREATE STREAM, but when you go to query it…
ksql> SELECT * FROM MY_FIRST_KSQL_STREAM;
…nothing happens. And because KSQL queries are continuous, your KSQL session appears to “hang.” That’s because KSQL is continuing to wait for any new messages to show you. So if your run a KSQL
SELECTand get no results back, what could be the reasons for that?
Robin gives us five reasons why this might be.