Apply Operator

Python Programming Learning Circle

Jun 22, 2021 · Databases

Decorrelation of Correlated Subqueries: Theory, Operators, and Optimization Rules

This article explains why correlated subqueries are a performance bottleneck, introduces the Apply (Correlated Join) operator, classifies subquery types, shows how to transform them into efficient joins, and discusses rule‑based push‑down techniques for Project, Filter, Aggregate, and Set operations.