ORDER BY Sorting Mechanisms in SQL constitutes a formal algorithmic procedure for arranging result sets within relational algebra based on specified key attributes and collation rules. The theory relies strictly on the stability properties inherent to certain implementation strategies, such as filesort operations or merge joins, to preserve relative row order during intermediate query processing steps where no explicit sort is requested. This concept resides within the domain of database management systems specifically under the subfield of relational calculus optimization and output specification logic.
Article: PostgreSQL Sort Performance and work_mem Tuning