SQL

Characteristics

• Declarative — describes the result, not the algorithm
• Set-based: operations apply to rows in bulk
• Standardised by ANSI, with dialect differences per engine
• Transactional, offering atomic multi-statement changes

Common uses

• Application data access in relational databases
• Reporting, dashboards and business analytics
• Data migrations and schema management
• ETL pipelines and warehouse transformations

Advantages

• One language works across most relational engines
• The planner optimises execution as data grows
• Transactions guarantee consistency across multiple changes
• Decades of tooling, documentation and expertise

Limitations

• Dialect differences complicate portability
• Poorly written queries can be catastrophically slow
• Awkward for hierarchical or graph-shaped data
• String-concatenated queries invite SQL injection

Examples

SELECT c.country,
       COUNT(*) AS orders,
       SUM(o.total) AS revenue
FROM orders o
JOIN customers c ON c.id = o.customer_id
WHERE o.created_at >= '2026-01-01'
GROUP BY c.country
HAVING COUNT(*) > 25
ORDER BY revenue DESC
LIMIT 10;

Frequently asked questions