Skill Request: Head First SQL

[ZLStas]

Skill Request: Head First SQL

Would love to see a skill that packages the key practices from Head First SQL into a reusable agent skill.

A skill for writing efficient, correct SQL — joins, indexes, transactions, and query optimization.

What this skill would cover

Resources

• Book: Head First SQL

---

Want to contribute this skill? See CONTRIBUTING.md for how to add a new skill.

[ZLStas]

@claude implement this

[claude]

Claude finished @ZLStas's task in 3m 45s —— View job • claude/issue-11-20260225-1603 • Create PR ➔

---

Implementing Head First SQL Skill

• Gather context (read CLAUDE.md and existing skills)
• Understand skill structure and format
• Create head-first-sql/SKILL.md (179 lines — query writing + review modes, patterns, anti-patterns)
• Create head-first-sql/examples/before.md (broken query with SELECT *, Cartesian join, NULL bug, N+1)
• Create head-first-sql/examples/after.md (same query fixed with explicit JOINs, correct NULL, aggregation)
• Create head-first-sql/evals/evals.json (5 evals: NULL comparison, WHERE vs HAVING, Cartesian product, missing transaction, well-written query recognition)
• Create head-first-sql/references/review-checklist.md
• Create head-first-sql/references/sql-patterns.md
• Update README.md skills table
• Update skill-router/references/skill-catalog.md
• Commit and push changes

Summary

Created the head-first-sql skill with the following structure:

head-first-sql/
├── SKILL.md                          # Query writing + SQL review modes
├── examples/
│   ├── before.md                     # Query with SELECT *, NULL bug, N+1, cross join
│   └── after.md                      # Fixed with explicit JOINs, IS NOT NULL, GROUP BY
├── evals/
│   └── evals.json                    # 5 evals covering common SQL pitfalls
└── references/
    ├── review-checklist.md           # Correctness, readability, performance, safety checklist
    └── sql-patterns.md               # JOIN, aggregation, NULL, transaction, index patterns

The skill covers the core Head First SQL topics: JOINs (INNER/LEFT/anti-join), aggregation with GROUP BY/HAVING, NULL handling, transactions, subqueries vs CTEs, index sargability, and schema design.