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.