Since this is a book about Cassandra and not targeted to users of any particular programming language or application framework, we will focus entirely on the database interactions that MyStatus will require. Code examples will be in Cassandra Query Language (CQL). Specifically, we'll use version 3.4.0 of CQL, which is available in Cassandra 3.0 and later versions.
As the name implies, CQL is heavily inspired by SQL; in fact, many CQL statements are equally valid SQL statements. However, CQL and SQL are not interchangeable. CQL lacks grammar for relational features such as JOIN statements, which are not possible in Cassandra. Conversely, CQL is not a subset of SQL; constructs for retrieving the update time of a given column, or performing an update in a lightweight transaction, which are available in CQL, do not have an SQL equivalent.
