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A lecture note on how indexing works with columns that have duplicate values, covering index selectivity and practical examples.

This lecture explains why databases fetch entire pages instead of individual rows when executing SQL queries, covering variable-sized rows, disk storage limits, and how indexes work.

Learn how databases solve modern data challenges through SQL querying, filtering, and aggregation using SQLite.

A clear explanation of how Repeatable Read and Snapshot Isolation work in databases, focusing on handling data changes during transactions.

A look at why PostgreSQL skips indexes for small tables and how outdated statistics can slow down queries after big data inserts.

Lecture clarifying that PostgreSQL planner uses abstract cost units rather than milliseconds, with examples showing how costs reflect I/O and CPU work.

Explains why PostgreSQL falls back to a bitmap heap scan instead of an index-only scan, focusing on MVCC visibility and the visibility map.

An overview of transaction isolation levels, their behaviors, and practical strategies to manage concurrency in real-world database systems.