Why data types matter

Concepts covered: sqlBasicTypes

Data types are not just labels. They fundamentally determine how your data is stored, processed, and queried. The database uses your type choice to decide everything from how much disk space to use, to whether math operations are allowed. SQL databases organize data into three fundamental categories. Every other type is a specialization of these: Type Mismatch Consequences Choosing the wrong type leads to unexpected behavior in operations like arithmetic and sorting. Arithmetic Proves the Type The type system enforces what operations are legal. Storing a number as text disables arithmetic and changes sort order, so the database treats "9" as greater than "10" alphabetically. Type mismatches are among the most common sources of data pipeline bugs. Catching them early at schema design time i

About This Interactive Section

This section is part of the Data Types: 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.

How DataDriven Lessons Work

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.