Database Types

Not all data is the same shape. Different database types are optimized for different data patterns.

The 6 Major Types

Type	Example	Data Shape	Use Case
Relational	PostgreSQL, MySQL	Tables with rows	Transactions, inventory
Document	MongoDB, Couchbase	JSON-like documents	User profiles, catalogs
Key-Value	Redis, DynamoDB	Key → value pairs	Cache, session store
Wide-Column	Cassandra, Bigtable	Rows with many columns	Time-series, IoT
Graph	Neo4j, ArangoDB	Nodes + edges	Social networks, recommendations
Time-Series	InfluxDB, TimescaleDB	Timestamp → value	Metrics, monitoring

Quick Decision Guide

flowchart TB
    Q1{"Data has strong<br/>relationships,<br/>needs JOINs?"}
    Q1 -->|Yes| SQL["Relational (PostgreSQL)"]
    Q1 -->|No| Q2{"Schema is<br/>flexible or<br/>changes often?"}

    Q2 -->|Yes| Q3{"Data structure<br/>looks like<br/>documents?"}
    Q2 -->|No| Q4{"Primary access<br/>is by key?"}

    Q3 -->|Yes| Doc["Document (MongoDB)"]
    Q3 -->|No| GraphQ{"Need to traverse<br/>relationships?"}
    GraphQ -->|Yes| Graph["Graph (Neo4j)"]

    Q4 -->|Yes| KV["Key-Value (Redis)"]
    Q4 -->|No| WC{"Massive write<br/>volume, time-ordered?"}
    WC -->|Yes| Col["Wide-Column (Cassandra)"]
    WC -->|No| TS["Time-Series (InfluxDB)"]

    style SQL fill:#7c3aed,color:#fff
    style Doc fill:#4f46e5,color:#fff
    style KV fill:#6366f1,color:#fff
    style Col fill:#8b5cf6,color:#fff
    style Graph fill:#059669,color:#fff
    style TS fill:#059669,color:#fff

Trade-offs

Database	Read Perf	Write Perf	Consistency	Scalability
Relational	Medium	Medium	Strong	Hard
Document	High	High	Tunable	Good
Key-Value	⚡ Very High	⚡ Very High	Usually eventual	Excellent
Wide-Column	High	⚡ Very High	Eventual	Excellent
Graph	Medium (traversal)	Low (nodes)	Strong	Hard
Time-Series	High (range)	⚡ Very High	Eventual	Good

In Simple Words

Use the database that matches your data shape — don’t force a square peg into a round hole.
Relational for structured, joined data. Document for JSON-like objects. KV for fast lookups.
Wide-column for write-heavy time-series. Graph for connected data (friends, recommendations).