SQL and Data Design

Core idea

SQL is a language for set operations and relational logic. It is not only about syntax; it is about modeling and operational correctness across joins, indexes, and transaction boundaries.

• Choose clear primary keys and enforce constraints.
• Measure query plans before adding more indexes.
• Use migrations and versioned schema changes.

Schema and query flow

1. Define entities and invariants first.
2. Write example data and expected responses.
3. Introduce indexes after observing real workload paths.
4. Audit constraints and cleanup jobs before scale.

Example: reporting query

CREATE TABLE feature_requests(
  id BIGSERIAL PRIMARY KEY,
  title TEXT NOT NULL,
  status TEXT NOT NULL,
  created_at TIMESTAMP NOT NULL DEFAULT NOW()
);

SELECT status, COUNT(*) AS total
FROM feature_requests
WHERE created_at >= NOW() - INTERVAL '14 days'
GROUP BY status
ORDER BY total DESC;

Checklist for production data

Area	What to verify
Integrity	Unique and foreign keys exist where needed.
Security	Parameter binding and role-based access control.
Performance	Slow query logs reviewed weekly.
Lifecycle	Archive and retention jobs are automated.

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