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DATABASES
UUIDs as Primary Keys in MySQL: A Practical Guide
When to use UUIDs as MySQL primary keys, how B+ trees react, why CHAR(36) hurts, and better options like BINARY(16), UUIDv7, ULIDs, and Snowflake IDs.
DATABASES
What Is Multitenancy? Rails Examples for SaaS
Clear definition of multitenancy vs user management, two patterns (row-level vs database-per-tenant), plus Rails examples using a School→Course→Lesson ERD and copy‑paste client answers.