In this SQL Server training video, instructor Peter Avila demonstrates how to utilize common table expressions (CTEs) to progressively convert one data structure to another. Using a real world example, Peter introduces a common problem in which the structure of the desired output and the structure of the data in the database are so different that the output cannot be obtained by a single transformation of the data from the database. Using a chain of CTEs, Peter shows how to break down the problem into smaller transformations and perform them step by step to obtain the desired structure in the output.