Cassandra（NoSQL数据库系统）怎么多表关联查询？
官方建议如下（简单的来说就是你最好把表设计成无关联的宽表，不支持join）：
Design Differences Between RDBMS and Cassandra
No joins
You cannot perform joins in Cassandra. If you have designed a data model and find that you need something like a join, you’ll have to either do the work on the client side, or create a denormalized second table that represents the join results for you. This latter option is preferred in Cassandra data modeling. Performing joins on the client should be a very rare case; you really want to duplicate (denormalize) the data instead.