Inside the Query Optimizer: How Engines Pick a Plan

This article is part 5 of a series on query engine design, detailing how query optimizers transform SQL into efficient execution plans. It covers the three stages of query processing (parse, logical plan, physical plan), rule-based optimization techniques like predicate pushdown and projection pruning, and cost-based optimization that searches for the best plan. Key topics include join order importance, cardinality estimation challenges, adaptive query execution, and the tradeoff between planning time and execution time. The article provides technical depth for understanding database performance tuning and query engine internals.