M query structure

• The great majority of queries created for Power BI will follow the let...in structure as per this recipe, as they contain multiple steps with dependencies among them.
• Individual expressions are separated by commas.
• The expression referred to following the in keyword is the expression returned by the query.
• The individual step expressions are technically "variables", and if the identifiers for these variables (the names of the query steps) contain spaces then the step is placed in quotes, and prefixed with a # sign as per the Filtered Rows step in Figure 10.