This book by Don Chamberlin (one of the designers of the original SQL database language) is the go-to source for developers and analysts who want to learn SQL++.
SQL++ combines the full power of SQL with the flexibility of JSON to provide a complete and efficient solution for querying JSON or semi-structured data in JSON form. This tutorial provides a thorough introduction to SQL++ for those with a working knowledge of SQL. In particular, it does an excellent job of highlighting the key data model and language differences that JSON brings and the resulting potential pitfalls – and avoidance patterns – to watch out for.