Database Reference
In-Depth Information
Relational joins
In real-world applications, different pieces of data relate to each other in a variety of ways.
Relational databases allow us to perform queries that make these relationships explicit, for
instance, to retrieve a set of events whose location is in the state of New York (this is as-
suming events and locations are different record types). Cassandra, however, is not a rela-
tional database, and does not support anything like joins. Instead, applications using Cas-
sandra typically denormalize data and make clever use of clustering in order to perform the
sorts of data access that would use a join in a relational database.
For data sets that aren't already denormalized, applications can also perform client-side
joins, which mimic the behavior of a relational database by performing multiple queries
and joining the results at the application level. Client-side joins are less efficient than read-
ing data that has been denormalized in advance, but offer more flexibility. We'll cover both
