Excellent demonstration of Oracle's inner workings! The modern Oracle uses a Cost-Based approach wherein the query optimizer will attempt to perform the lowest

Excellent demonstration of Oracle's inner workings! The modern Oracle uses a Cost-Based approach wherein the query optimizer will attempt to perform the lowest-cost opration to satisfy the query. If that means performing a full-table scan as opposed to utilizing an index, then this is what will be done. Statistics, data histograms, parameters (such as OPTIMIZER_ INDEX_COST_ADJ) all come into play.