SQL vs NoSQL Databases

Deciding the correct database is the most essential part of system design.

There are two categories of the database which are SQL (Structured Query Language) and NoSQL (Not Only SQL). Both have their unique features, and weakness. Choosing the right one is a core architectural decision in system design.

The choice between the two affects not only how data is stored but also how your application scales, performs, and evolves over time.

What Are SQL Databases?

SQL (Structured Query Language) databases, also known as relational databases, store data in table with fixed schemas.

Key Characteristics:

1. Structured Schema: Tables with predefined columns and data types.
2. ACID Transactions: Guarantees Atomicity, Consistency, Isolation, Durability, making SQL ideal for transactional systems.
3. Strong Relationships: Foreign keys and joins enable complex relationships between tables.
4. Query Language: Use SQL for data manipulation and queries.
5. Mature Ecosystem: Long-standing tools for backup, monitoring, and scaling.

Popular SQL Databases:

• MySQL
• PostgreSQL
• Oracle Database
• Microsoft SQL Server

Pros of SQL in System Design

• Data Integrity & Consistency: Ensures transactional reliability.
• Complex Queries: JOINs and aggregates simplify querying relational data.
• Mature Ecosystem: Well-tested, reliable, and supported in production.
• Predictable Behavior: Easy reasoning for financial, inventory, or ERP systems.

Cons of SQL:

• Scalability Challenges: Vertical scaling is often required; horizontal sharding is complex.
• Rigid Schema: Schema changes require migrations, which can be costly.
• Not ideal for Unstructured Data: JSON blobs or rapidly changing schema are harder to manage.

SQL vs NoSQL