Human Factors Comparison of a Procedural and a Nonprocedural Query Language
ACM Transactions on Database Systems
Two experiments testing the ability of subjects to write queries in two different query languages were run. The two languages, SQL and TABLET, differ primarily in their procedurality; both languages use the relational data model, and their Halstead levels are similar. Constructs in the languages which do not affect their procedurality are identical....
Welty, C. & Stemple, D.W. Human factors comparison of a procedural and a nonprocedural query language. ACM Transactions on Database Systems, 6(4), 626-649. https://doi.org/10.1145/319628.319656