Cost

A relative metric of which query plan is better, based on data distribution statistics. Cost does not translate into time but is an internal estimate that the query optimizer uses to compare different plans. Costs are not relative to the overall estimated run time of queries, rather they are an estimate of the overall resources that the query plan will use. If the cost of one plan is twice as large as the cost of a second plan, that does not mean the second plan will take twice as long to run.