Query Optimization

0 lessons

1 system design

4 community items

query-optimization

System Design

1 article

Database Indexing & Query Optimization

Indexes turn O(N) full-table scans into O(log N) lookups, but every index costs storage and slows writes. This lesson teaches how B-tree and hash indexes work, when to use composite or covering indexes, how to read an EXPLAIN plan, and the common indexing mistakes that cause production outages. By the end you can defend any indexing decision in an interview and diagnose a slow query in production.

332

Community

4 items

Article

N+1 Queries: Detection and Prevention

What an N+1 query is, why ORMs hide them, the four ways to fix them, and the simple logging change that has caught every N+1 I have shipped since I added it.

806

4.5 (10)

Apr 23, 2026

by @adaezeaziz

Question Bundle

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Django ORM N+1 and prefetch_related Drill

Four questions on Django ORM patterns I keep flagging in code review: spotting N+1 in templates, choosing select_related vs prefetch_related, slicing prefetches, and avoiding the .count() trap.

412

4.4 (9)

Apr 16, 2026

by @freyadiallo

Article

MongoDB Aggregation Pipelines, by Example

Match, group, lookup, project, the four stages I use 90% of the time. Real pipelines for funnel analysis, leaderboard, and a one-stage join, with the gotchas that surprise SQL refugees.

582

4.5 (11)

Feb 1, 2026

by @fatimapark

Article

Database Indexes Explained with Real EXPLAIN Output

What an index actually is, how the planner picks one, and the EXPLAIN output I read every day. Postgres examples, real numbers, and the three indexing mistakes I keep finding in code review.

1.1k

4.4 (16)

Dec 2, 2025

by @theowatanabe