Primary

Constraints and Keys

Learn how PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, DEFAULT, and NOT NULL constraints enforce data integrity directly at the database layer.

Constraints in Depth

A thorough look at PostgreSQL's constraint types -- PRIMARY KEY, FOREIGN KEY, CHECK, UNIQUE, NOT NULL, and EXCLUDE -- and how they enforce data integrity at th…

Shards and Replicas

How Elasticsearch splits indices into shards for scalability and duplicates them as replicas for resilience and read throughput.

Constructors in Kotlin (Primary and Secondary)

Understand how primary and secondary constructors initialize Kotlin objects, including init blocks and constructor delegation.

Primary and Foreign Keys

Understand how primary keys uniquely identify rows and foreign keys enforce relationships between tables.