# sql-best-practices

SQL guidelines for coding agents: covers query formatting, indexing, explicit joins, and injection defenses for database workflows.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 790 installs · ★ 286
- Author: Mindrally
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/Mindrally/skills/tree/HEAD/sql-best-practices/SKILL.md
- Updated: 2026-10-08
- HTML: https://affpapa.org/en/nevibecode/skills/sql-best-practices

## What it does

This skill guides coding assistants to produce clean, safe database queries. It enforces listing columns explicitly instead of running `SELECT *` in production. For subqueries checking existence, it prioritizes `EXISTS` over `IN`. Key clauses sit on separate lines, and filter logic avoids functions wrapped around indexed columns.

Join conventions require explicit `INNER` or `OUTER` syntax rather than comma-separated tables in `WHERE` clauses. Modification operations follow strict boundaries. `UPDATE` and `DELETE` statements must include targeted `WHERE` conditions, while `INSERT` operations require explicit column names.

Direct concatenation of user input into queries is strictly barred, making prepared statements mandatory for security.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill sql-best-practices -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/sql-best-practices/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/sql-best-practices/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill sql-best-practices -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/sql-best-practices/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill sql-best-practices -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/sql-best-practices/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install Mindrally/skills sql-best-practices
```

2. **Manually: put the files in place**
- File: `.github/skills/sql-best-practices/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill sql-best-practices -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/Mindrally/skills --path sql-best-practices
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/sql-best-practices/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill sql-best-practices -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/Mindrally/skills/tree/HEAD/sql-best-practices/SKILL.md

## When to use it
- Refactor implicit joins into explicit `INNER JOIN` statements
- Secure raw queries with parameter binding against SQL injection
- Structure transactions with rollback handling for data consistency
- Add pagination with `LIMIT` and `OFFSET` without selecting unnecessary columns

## Example prompts
- Refactor this legacy query to use explicit `INNER JOIN` syntax and proper table aliases
- Convert this raw input query into a parameterized prepared statement
- Check my `DELETE` statement to ensure safe filtering and soft delete patterns

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 3facb66f3bf7b047.

BEGIN THIRD-PARTY FILE 3facb66f3bf7b047
````text
---
name: sql-best-practices
description: SQL development best practices for writing efficient, secure, and maintainable database queries
metadata:
  maintainer: Mindrally
  source: https://github.com/Mindrally/skills
---

# SQL Best Practices

## Core Principles

- Write clear, readable SQL with consistent formatting and meaningful aliases
- Prioritize query performance through proper indexing and optimization
- Implement security best practices to prevent SQL injection
- Use transactions appropriately for data integrity
- Document complex queries with inline comments

## Query Writing Standards

### Formatting and Style

- Use uppercase for SQL keywords (SELECT, FROM, WHERE, JOIN)
- Place each major clause on a new line for readability
- Use meaningful table aliases (e.g., `customers AS c` not `customers AS x`)
- Indent subqueries and nested conditions consistently
- Align column lists and conditions for visual clarity

```sql
SELECT
    c.customer_id,
    c.customer_name,
    o.order_date,
    o.total_amount
FROM customers AS c
INNER JOIN orders AS o ON c.customer_id = o.customer_id
WHERE o.order_date >= '2024-01-01'
    AND o.status = 'completed'
ORDER BY o.order_date DESC;
```

### Column Selection

- Avoid `SELECT *` in production code; explicitly list required columns
- Use column aliases to clarify output: `SELECT first_name AS "First Name"`
- Consider the order of columns in SELECT for logical grouping

### Filtering and Conditions

- Place most restrictive conditions first in WHERE clauses
- Use appropriate operators: prefer `IN` over multiple `OR` conditions
- Use `EXISTS` instead of `IN` for subqueries when checking existence
- Avoid functions on indexed columns in WHERE clauses when possible
- Use parameterized queries to prevent SQL injection

```sql
-- Preferred: Use EXISTS for existence checks
SELECT c.customer_name
FROM customers AS c
WHERE EXISTS (
    SELECT 1 FROM orders AS o
    WHERE o.customer_id = c.customer_id
    AND o.order_date > '2024-01-01'
);

-- Avoid: Function on indexed column
WHERE YEAR(order_date) = 2024

-- Preferred: Range comparison
WHERE order_date >= '2024-01-01' AND order_date < '2025-01-01'
```

## Join Best Practices

- Always use explicit JOIN syntax instead of implicit joins in WHERE
- Specify join type explicitly (INNER, LEFT, RIGHT, FULL OUTER)
- Order joins from largest to smallest table when possible
- Use appropriate join types based on data requirements
- Be cautious with CROSS JOINs; ensure they are intentional

```sql
-- Explicit join (preferred)
SELECT c.name, o.order_id
FROM customers AS c
INNER JOIN orders AS o ON c.customer_id = o.customer_id;

-- Avoid implicit join
SELECT c.name, o.order_id
FROM customers c, orders o
WHERE c.customer_id = o.customer_id;
```

## Performance Optimization

### Indexing Guidelines

- Create indexes on columns used in WHERE, JOIN, and ORDER BY clauses
- Consider composite indexes for multi-column queries
````
END THIRD-PARTY FILE 3facb66f3bf7b047

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