Access Paths, Index Scan, Aggregates

General Query Optimizers

1. Apply blind heuristics (e.g., push down selections)
2. Enumerate all possible execution plans by varying (or for a reasonable subset)
   • Join/Union Evaluation Order (commutativity, associativity, distributivity)
   • Algorithms for Joins, Aggregates, Sort, Distinct, and others
   • Data Access Paths
3. Estimate the cost of each execution plan
4. Pick the execution plan with the lowest cost