When the "Missing" Set Is Itself Filtered

Concepts covered: sqlExists

After correctness, the interviewer escalates to performance. The follow-up: 'how does the query planner execute this on a billion-row table?' All three forms can produce the same physical plan on a modern optimizer; they can also fall back to nested loops on an older one. Knowing when each plan applies, and what to do when the optimizer picks the slow one, is the depth this question rewards at the mid-and-above level. The three execution plans you should know Hash anti-join: build a hash table of the right side, scan the left side, emit each left row that does not have a hash match. O(N + M), memory bounded by the size of the right side. Merge anti-join: sort both inputs on the join key, walk them in tandem, emit left rows that do not match. O(N log N + M log M), good when inputs are alrea

About This Interactive Section

This section is part of the Anti-Join: 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 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.