Query Execution Order

Concepts covered: sqlExecutionOrder

Understanding Execution Order Walk through this example to see how the CTE executes before the outer query, not after it. Basic Example This example shows how a CTE executes first to filter logs, then the outer query applies an additional filter on the result. The CTE executes first to produce the temporary dataset. The outer query then filters from it. Practical Implications Understanding execution order helps you avoid common pitfalls like referencing aliases before they exist. Real-World Example When working with device logs, intermediate results must exist before applying filters or aggregations. Ignoring execution order can lead to errors or incorrect results. Understanding the sequence of execution ensures each step behaves correctly and can be reused for other tasks. Here is the ful

About This Interactive Section

This section is part of the Query Structure: Intermediate 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.