Cassandra Query Language (CQL) is the default and primary interface into the Cassandra DBMS. Using CQL is similar to using SQL (Structured Query Language). CQL and SQL share the same abstract idea of a table constructed of tables and rows. The main difference from SQL is that Cassandra does not support joins or subqueries, except for batch analysis through Hive. Instead, Cassandra emphasizes denormalization through CQL features like collections and clustering specified at the schema level.
CQL is the recommended way to interact with Cassandra. The simplicity of reading and using CQL is an advantage over of modern Cassandra over older Cassandra APIs.