Database Design Skill for Cursor
Schema design, normalization, indexing, migrations, and query optimization for SQL and NoSQL
Install
one command, takes just this skill from the repositorynpx skills add https://github.com/cosmicstack-labs/mercury-agent-skills --skill database-designThe instruction itself
7 sections, as written by the authorDatabase Design
Design efficient, scalable database schemas.
Normalization
| Normal Form | Rule | Violation Example |
|-------------|------|-------------------|
| 1NF | Atomic columns, no repeating groups | phone_numbers: "555-0100,555-0200" |
| 2NF | 1NF + all non-key cols depend on full PK | Orders table with product details |
| 3NF | 2NF + no transitive dependencies | Employee with department_name (dept info in dept table) |
When to denormalize: Read-heavy workloads, reporting, caching layers.
Indexing Strategy
Index Types
| Index | Use Case | Tradeoff |
|-------|----------|----------|
| B-Tree | General purpose, equality + range | Default, usually best |
| Hash | Equality only | Fast lookups, no sorting |
| GIN | Array/JSON | Slightly slower writes |
| BRIN | Huge sorted tables | Very small size |
Rules
- Index columns used in WHERE, JOIN, ORDER BY
- Index foreign keys
- Covering indexes for frequent queries
- Don't over-index (slows writes, uses space)
- Drop unused indexes (use pg_stat_user_indexes)
Migrations
- One file per change, sequential naming
- Always reversible (up/down pair)
- Test on staging before production
- Run in transactions where possible
- Avoid locking tables on large tables (use pt-online-schema-change)
Query Optimization
- EXPLAIN ANALYZE every slow query
- Look for: Seq scans, nested loops, temp files
- Common fixes: missing index, bad join order, OR conditions
- N+1 problem: batch find / includes / joins
- Limit offsets for pagination (use cursor-based)
Other skills for the same job
different authors, same section of the catalogue
Efficient database search tool for bioRxiv preprint server. Use this skill when searching for life sciences preprints by keywords, authors, date ranges, or categories, retrieving paper metadata, downloading PDFs, or conducting literature reviews.
Access BRENDA enzyme database via SOAP API. Retrieve kinetic parameters (Km, kcat), reaction equations, organism data, and substrate-specific enzyme information for biochemical research and metabolic pathway analysis.
Access ClinPGx pharmacogenomics data (successor to PharmGKB). Query gene-drug interactions, CPIC guidelines, allele functions, for precision medicine and genotype-guided dosing decisions.
Query NCBI ClinVar for variant clinical significance. Search by gene/position, interpret pathogenicity classifications, access via E-utilities API or FTP, annotate VCFs, for genomic medicine.
Access COSMIC cancer mutation database. Query somatic mutations, Cancer Gene Census, mutational signatures, gene fusions, for cancer research and precision oncology. Requires authentication.
Query Ensembl genome database REST API for 250+ species. Gene lookups, sequence retrieval, variant analysis, comparative genomics, orthologs, VEP predictions, for genomic research.
Query openFDA API for drugs, devices, adverse events, recalls, regulatory submissions (510k, PMA), substance identification (UNII), for FDA regulatory data analysis and safety research.
Query NCBI Gene via E-utilities/Datasets API. Search by symbol/ID, retrieve gene info (RefSeqs, GO, locations, phenotypes), batch lookups, for gene annotation and functional analysis.
How to use it
Take cosmicstack-labs/database-design from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.