M Let Expressions

Introduction to M Let Expressions

M Let expressions are a powerful feature in the M language (used in Power Query) that allow developers to create structured queries with reusable steps. By using let expressions, you can break down complex queries into manageable parts, improving readability and maintainability.

Basic Structure of Let Expressions

A let expression typically consists of two parts: a let clause and an in clause. The let clause is where you define variables and perform intermediate calculations, while the in clause specifies the final expression that uses the defined variables.

Step-by-Step Example

Let's break down the example above:

• The Source variable retrieves data from an Excel table named Table1.
• The FilteredRows variable filters the rows where the Sales column values are greater than 1000.
• The Result variable sorts the filtered data by the Sales column.
• The in clause specifies that the final output of the expression is the Result variable.

Benefits of Using Let Expressions

Using let expressions offers several advantages:

• Improved Readability: By breaking down queries into steps, you make the logic easier to follow.
• Reusability: Intermediate variables can be reused in different parts of the expression.
• Maintainability: If you need to update a part of the query, you can do so in the let clause, reducing redundancy.

Common Use Cases

Let expressions are commonly used for:

• Data transformation and cleaning
• Aggregating data from various sources
• Creating complex calculations without repeating code