Couchbase Server 5.5 introduces several new querying features aimed at enhancing flexibility and performance, including ANSI JOINs, HASH joins, and aggregate pushdowns. ANSI JOINs now allow more standard-compliant syntax and greater flexibility by removing previous constraints, while HASH joins can improve performance for certain types of joins by constructing an in-memory hash table, although these require explicit invocation and are available only in the Enterprise Edition. Aggregate pushdowns improve the performance of aggregation operations by enabling the index service to handle grouping tasks, significantly reducing execution time when indexes are properly utilized. The release aims to provide a more natural experience for users familiar with relational databases and includes various examples to demonstrate the practical application of these new features using the "travel-sample" dataset.