Get sql records count

In this case, you will need some extra steps. You could try something like:

You have an ExecuteSQLRecord or ExecuteSQL, configured with the Database Connection Pooling Service and the Record Writer (if using ExecuteSQLRecord).

Next, I would link the success queue to an ExtractText Processor. In this Processor I would add a new property called number_of_rows having the value " .* ". This will extract the value returned by count(*) and save it as an attribute in your FlowFile.

Once you did this, you can link the success queue to an RouteOnAttribute Processor. Here, you will define a new property named bigger_as_zero and use the NiFi's EL to validate if the attribute is bigger than zero or not.

If bigger, you will send that message to the processor in which you have linked this queue. Otherwise, meaning that the value is zero, you can route the unmatched queue to another ExecuteSQL/ExecuteSQLRecord. You could also apply NiFi's EL to check if the value is exactly zero, if that is what you are looking for and route the file accordingly.

NiFi's EL: https://nifi.apache.org/docs/nifi-docs/html/expression-language-guide.html

Everything mentioned above has to be done, in addition to what @SAMSAL already said, with the fact that you need to modify you running schedule from 0 seconds to a greater value. 0 means that you will constantly execute this SQL Record. Here you will have to modify the value based on your project's requirements.