Comments can now be used in NRQL queries to easily add context to a complex query, comment out a line temporarily, or just explain the events or attributes being queried in NRDB.
Both single and multi-line comments can be added to NRQL queries. Single-line comments start with -- or //, after which everything will be ignored up to the end of the line. Multi-line comments are enclosed within /* and */ and everything in between will be ignored:

Read more in our NRQL Reference to get started.