The goal was to make a way to do join operations in Cassandra, even though it normally can't. They made a library to add join functions to Cassandra, focusing on how Cassandra stores data and figuring out the best way to do joins. They found that two types of join methods, hybrid hash join and nested loop join, work well in Cassandra. The library they created can do inner and outer joins on data in different ways. The hybrid hash join works fast with lots of data, while the nested loop join is slower with large amounts of data.