Expressions in SELECT

Expressions transform data on the fly, letting you compute totals, differences, and other derived values directly in your query. An expression is any combination of values, operators, and functions that the database evaluates to produce a result. For example, "price + tax" is an expression that adds two column values together. SQL can calculate new values as part of the results using expressions. Common Operations SQL supports standard arithmetic operators that let you perform calculations directly within your queries. Practice: Expressions Put your expression skills to work by calculating a total cost from quantity and unit price. Expressions let you compute answers directly in the database rather than pulling raw numbers into a spreadsheet and calculating there, which is both faster and

About This Interactive Section

This section is part of the Query Structure: Beginner 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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DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.