STRING types (VARCHAR)

String literals in SQL are enclosed in single quotes. Double quotes are reserved for identifiers (table and column names). This is a common source of confusion for beginners. Choosing String Types Different string types suit different use cases based on length variability and storage needs. One of the most common string operations is measuring how long a value is. Try it yourself. Single quotes delimit string literals in SQL while double quotes delimit identifiers like table and column names. Mixing them up is one of the most frequent syntax errors for SQL beginners.

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.