supabase-postgres-best-practices/skills/postgres-best-practices/rules/_contributing.md

Writing Guidelines for Postgres Rules

This document provides guidelines for creating effective Postgres best practice rules that work well with AI agents and LLMs.

Key Principles

1. Concrete Transformation Patterns

Show exact SQL rewrites. Avoid philosophical advice.

Good: "Use WHERE id = ANY(ARRAY[...]) instead of WHERE id IN (SELECT ...)" Bad: "Design good schemas"

2. Error-First Structure

Always show the problematic pattern first, then the solution. This trains agents to recognize anti-patterns.

**Incorrect (sequential queries):** [bad example]

**Correct (batched query):** [good example]

3. Quantified Impact

Include specific metrics. Helps agents prioritize fixes.

Good: "10x faster queries", "50% smaller index", "Eliminates N+1" Bad: "Faster", "Better", "More efficient"

4. Self-Contained Examples

Examples should be complete and runnable (or close to it). Include CREATE TABLE if context is needed.

-- Include table definition when needed for clarity
CREATE TABLE users (
  id bigint PRIMARY KEY,
  email text NOT NULL,
  deleted_at timestamptz
);

-- Now show the index
CREATE INDEX users_active_email_idx ON users(email) WHERE deleted_at IS NULL;

5. Semantic Naming

Use meaningful table/column names. Names carry intent for LLMs.

Good: users, email, created_at, is_active Bad: table1, col1, field, flag

---

Code Example Standards

SQL Formatting

-- Use lowercase keywords, clear formatting
CREATE INDEX CONCURRENTLY users_email_idx
  ON users(email)
  WHERE deleted_at IS NULL;

-- Not cramped or ALL CAPS
CREATE INDEX CONCURRENTLY USERS_EMAIL_IDX ON USERS(EMAIL) WHERE DELETED_AT IS NULL;

Comments

• Explain why, not what
• Highlight performance implications
• Point out common pitfalls

Language Tags

• sql - Standard SQL queries
• plpgsql - Stored procedures/functions
• typescript - Application code (when needed)
• python - Application code (when needed)

---

When to Include Application Code

Default: SQL Only

Most rules should focus on pure SQL patterns. This keeps examples portable.

Include Application Code When:

• Connection pooling configuration
• Transaction management in application context
• ORM anti-patterns (N+1 in Prisma/TypeORM)
• Prepared statement usage

Format for Mixed Examples:

**Incorrect (N+1 in application):**

```typescript
for (const user of users) {
  const posts = await db.query("SELECT * FROM posts WHERE user_id = $1", [
    user.id,
  ]);
}
```

Correct (batch query):

const posts = await db.query("SELECT * FROM posts WHERE user_id = ANY($1)", [
  userIds,
]);

---

Impact Level Guidelines

Level	Improvement	Use When
CRITICAL	10-100x	Missing indexes, connection exhaustion, sequential scans on large tables
HIGH	5-20x	Wrong index types, poor partitioning, missing covering indexes
MEDIUM-HIGH	2-5x	N+1 queries, inefficient pagination, RLS optimization
MEDIUM	1.5-3x	Redundant indexes, query plan instability
LOW-MEDIUM	1.2-2x	VACUUM tuning, configuration tweaks
LOW	Incremental	Advanced patterns, edge cases

---

Reference Standards

Primary Sources:

• Official Postgres documentation
• Supabase documentation
• Postgres wiki
• Established blogs (2ndQuadrant, Crunchy Data)

Format:

Reference:
[Postgres Indexes](https://www.postgresql.org/docs/current/indexes.html)

---

Review Checklist

Before submitting a rule:

• Title is clear and action-oriented
• Impact level matches the performance gain
• impactDescription includes quantification
• Explanation is concise (1-2 sentences)
• Has at least 1 Incorrect SQL example
• Has at least 1 Correct SQL example
• SQL uses semantic naming
• Comments explain why, not what
• Trade-offs mentioned if applicable
• Reference links included
• npm run validate passes
• npm run build generates correct output