SQL, Streaming Expressions on system signals collection

Issue:

The SQL service does not work on the system "_signals" collection due to the signals collection not having the "random" field configured OOTB

Environment:

Fusion 5.2

Resolution:

You need to add the following to the "_signals" managed-schema.xml:

<dynamicField name="random_*" type="random"/>

Cause:

Essentially the problem here is the SQL service uses streaming expressions in Solr to complete it's query. In this case it uses the stream source called "random", which requires the above to be a field in the schema.xml. Else it fails