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How it works...
Two of the top performance and scalability features of M's engine are Query Folding and Lazy Evaluation. If possible, the M queries developed in Power BI Desktop are converted (folded) into SQL statements and passed to source systems for processing. M can also reduce the required resources for a given query by ignoring any unnecessary or redundant steps (variables).
M is a case-sensitive language. This includes referencing variables in M expressions ( RenameColumns versus Renamecolumns) as well as the values in M queries. For example, the values "Apple" and "apple" are considered unique values in an M query; the Table.Distinct() function will not remove rows for one of the values.
Variable names in M expressions cannot have spaces without a hash sign and double quotes. Per Figure 10, when the Query Editor graphical interface is used to create M queries this syntax is applied automatically, along with a name describing the M transformation applied. Applying short, descriptive variable names (with no spaces) improves the readability of M queries. See the Strengthening Data Import and Integration Processes recipe in Chapter 11, Enhancing and Optimizing Existing Power BI Solutions for additional details.
Variable names in M expressions cannot have spaces without a hash sign and double quotes. Per Figure 10, when the Query Editor graphical interface is used to create M queries this syntax is applied automatically, along with a name describing the M transformation applied. Applying short, descriptive variable names (with no spaces) improves the readability of M queries. See the Strengthening Data Import and Integration Processes recipe in Chapter 11, Enhancing and Optimizing Existing Power BI Solutions for additional details.