The EXPLAIN request modifier that precedes any SQL request causes Teradata Database to display the execution plan for that request. The request itself is not submitted for execution.
When you perform an EXPLAIN against any SQL request, that request is parsed and optimized. The access and join plans generated by the Optimizer are returned in the form of a text file that explains the (possibly parallel) steps used in the execution of the request. Also included is the relative cost required to complete the request given the statistics with which the Optimizer had to work. If the statistics are not reasonably accurate, the cost estimate may not be accurate.