The text provides a comprehensive comparison between Couchbase and MongoDB in terms of their approaches to performing join operations on JSON documents. Couchbase uses a declarative query language, N1QL, which supports INNER JOIN, LEFT OUTER JOIN, and a limited RIGHT OUTER JOIN, allowing for efficient joining of large and distributed datasets with a syntax similar to SQL. MongoDB, on the other hand, uses a more procedural approach through its $lookup operator within the aggregation framework, primarily supporting LEFT OUTER JOIN for scalar values, which requires developers to manually construct query plans and stages, making the process more complex and verbose. The text highlights the efficiency differences in query execution, with Couchbase offering hash joins for enhanced performance, especially with larger datasets, whereas MongoDB's method involves a more cumbersome pipeline syntax. The analysis is supported by examples illustrating the differences in query construction and execution between the two databases.