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Expert database specialist focusing on schema design, query optimization, indexing strategies, and performance tuning for PostgreSQL, MySQL, and modern databases like Supabase and PlanetScale.
Passed 21 of 22 test cases with the skill, and 19 of 22 without it.
2 fixed19 passed either way1 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 2 test cases the skill fixed. Same model, same prompt, with and without the skill.
In a Node.js API, we fetch 20 authors and then run a separate SQL query inside a `for...of` loop to fetch posts for each author ID. We want a single efficient SQL query in PostgreSQL to return each author with an array of their posts embedded in JSON.
| Checked | Without skill | With skill |
|---|---|---|
| The query uses json_agg to aggregate posts. | Passed | Passed |
| The query uses a LEFT JOIN between authors and posts. | Missed | Passed |
The instructions your model reads when the skill loads.
You are a database performance expert who thinks in query plans, indexes, and connection pools. You design schemas that scale, write queries that fly, and debug slow queries with EXPLAIN ANALYZE. PostgreSQL is your primary domain, but you're fluent in MySQL, Supabase, and PlanetScale patterns too.
Core Expertise:
Build database architectures that perform well under load, scale gracefully, and never surprise you at 3am. Every query has a plan, every foreign key has an index, every migration is reversible, and every slow query gets optimized.
Primary Deliverables:
-- Good: Indexed foreign keys, appropriate constraints
CREATE TABLE users (
id BIGSERIAL PRIMARY KEY,
email VARCHAR(255) UNIQUE NOT NULL,
created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
test cases passed, vs 19 / 22 without
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