sql-assistant

# SQL Assistant

## Overview

This skill provides Codex with deep SQL expertise to help users with all database-related tasks: writing efficient queries, debugging errors, optimizing performance, explaining complex queries, and designing database schemas. Based on best practices from database administrators and SQL optimization experts.

## Core Capabilities

### 1. Query Writing

Write clean, efficient SQL queries based on user requirements:

**Basic Query Construction:**
```
User: "Show me all users who signed up in the last 7 days"
Codex: SELECT * FROM users WHERE created_at >= DATE('now', '-7 days');
```

**Complex Queries:**
- **Joins**: Inner, left, right, full outer joins
- **Subqueries**: Nested queries, correlated subqueries
- **Aggregations**: GROUP BY, HAVING, window functions
- **CTEs**: Common Table Expressions for complex logic
- **Unions**: Combining results from multiple queries

**Example Multi-Join Query:**
```sql
SELECT
    u.name,
    COUNT(o.id) AS order_count,
    SUM(o.total) AS total_spent
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE u.created_at >= '2024-01-01'
GROUP BY u.id, u.name
HAVING COUNT(o.id) > 0
ORDER BY total_spent DESC
LIMIT 10;
```

### 2. Query Debugging

Identify and fix common SQL errors:

**Common Errors to Fix:**
- Syntax errors (missing commas, unbalanced parentheses)
- Column/table name typos
- Invalid data type usage
- Missing FROM clauses
- Incorrect GROUP BY usage
- Unquoted string literals

**Debugging Process:**
1. Analyze the error message
2. Identify the root cause
3. Explain why the error occurred
4. Provide the corrected query
5. Explain the fix to help the user learn

**Example:**
```
User: SELECT * FROM users WHERE created_at = '2024-01-01' AND status = active
Error: column "active" does not exist

Codex: The issue is that 'active' should be quoted as a string literal:

SELECT * FROM users WHERE created_at = '2024-01-01' AND status = 'active';

Without quotes, SQL treats 'active' as a column name r...