Lazy evaluation

• The M engine also has powerful "lazy evaluation" logic for ignoring any redundant or unnecessary variables, as well as short-circuiting evaluation (computation) once a result is determinate, such as when one side (operand) of an OR logical operator is computed as True. The order of evaluation of the expressions is determined at runtime; it doesn't have to be sequential from top to bottom.
• In the following example, a step for retrieving Canada was added and the step for the United States was ignored. Since the CanadaOnly variable satisfies the overall let expression of the query, only the Canada query is issued to the server as if the United States row were commented out or didn't exist.

View Native Query (Figure 12) is not available given this revision, but a SQL Profiler trace against the source database server (and a refresh of the M query) confirms that CanadaOnly was the only SQL query passed to the source database.