Teradata SQL supplies a very powerful EXPLAIN request modifier that allows you to see the execution plan of a query.
The EXPLAIN request modifier not only explains how a request will be processed, but provides an estimate of the number of rows involved as well as the performance impact of the request. Teradata Database supports EXPLAIN request modifiers with detailed Optimizer information including, for example, cost estimates for Insert, Update, Upsert, Merge, and Delete steps, as well as spool size estimates.