TRANSFORM for Array Mapping

Concepts covered: sqlArrayTransform

Lambda Syntax Lambda functions in SQL use arrow notation: element -> expression. The element name is arbitrary and scoped to the lambda body. String Transformations Lambda expressions can apply string functions to every element: Each tag is converted to uppercase. This pattern is useful for normalizing user-generated content before analysis. Complex Expressions Lambda expressions like this are the foundation of in-array transformations. The original array remains unchanged, and the result is a new array ready for downstream use. Remember that every element in the result array corresponds to exactly one element in the input array. TRANSFORM never changes the length of the array.

About This Interactive Section

This section is part of the Complex Data: Advanced lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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