SQL Code Review

SQL Code Review

Perform a thorough SQL code review of ${selection} (or entire project if no selection) focusing on security, performance, maintainability, and database best practices.

🔒 Security Analysis

SQL Injection Prevention

-- ❌ CRITICAL: SQL Injection vulnerability
query = "SELECT * FROM users WHERE id = " + userInput;
query = f"DELETE FROM orders WHERE user_id = {user_id}";

-- ✅ SECURE: Parameterized queries
-- PostgreSQL/MySQL
PREPARE stmt FROM 'SELECT * FROM users WHERE id = ?';
EXECUTE stmt USING @user_id;

-- SQL Server
EXEC sp_executesql N'SELECT * FROM users WHERE id = @id', N'@id INT', @id = @user_id;

Access Control & Permissions

• Principle of Least Privilege: Grant minimum required permissions
• Role-Based Access: Use database roles instead of direct user permissions
• Schema Security: Proper schema ownership and access controls
• Function/Procedure Security: Review DEFINER vs INVOKER rights

Data Protection

• Sensitive Data Exposure: Avoid SELECT * on tables with sensitive columns
• Audit Logging: Ensure sensitive operations are logged
• Data Masking: Use views or functions to mask sensitive data
• Encryption: Verify encrypted storage for sensitive data

⚡ Performance Optimization

Query Structure Analysis

-- ❌ BAD: Inefficient query patterns
SELECT DISTINCT u.* 
FROM users u, orders o, products p
WHERE u.id = o.user_id 
AND o.product_id = p.id
AND YEAR(o.order_date) = 2024;

-- ✅ GOOD: Optimized structure
SELECT u.id, u.name, u.email
FROM users u
INNER JOIN orders o ON u.id = o.user_id
WHERE o.order_date >= '2024-01-01' 
AND o.order_date < '2025-01-01';

Index Strategy Review

• Missing Indexes: Identify columns that need indexing
• Over-Indexing: Find unused or redundant indexes
• Composite Indexes: Multi-column indexes for complex queries
• Index Maintenance: Check for fragmented or outdated indexes

Join Optimization

• Join Types: Verify appropriate join types (INNER vs LEFT vs EXISTS)
• Join Order: Optimize for smaller result sets first
• Cartesian Products: Identify and fix missing join conditions
• Subquery vs JOIN: Choose the most efficient approach

Aggregate and Window Functions

-- ❌ BAD: Inefficient aggregation
SELECT user_id, 
       (SELECT COUNT(*) FROM orders o2 WHERE o2.user_id = o1.user_id) as order_count
FROM orders o1
GROUP BY user_id;

-- ✅ GOOD: Efficient aggregation
SELECT user_id, COUNT(*) as order_count
FROM orders
GROUP BY user_id;

🛠️ Code Quality & Maintainability

SQL Style & Formatting

-- ❌ BAD: Poor formatting and style
select u.id,u.name,o.total from users u left join orders o on u.id=o.user_id where u.status='active' and o.order_date>='2024-01-01';

-- ✅ GOOD: Clean, readable formatting
SELECT u.id,
       u.name,
       o.total
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE u.status = 'active'
  AND o.order_date >= '2024-01-01';

Naming Conventions

• Consistent Naming: Tables, columns, constraints follow consistent patterns
• Descriptive Names: Clear, meaningful names for database objects
• Reserved Words: Avoid using database reserved words as identifiers
• Case Sensitivity: Consistent case usage across schema

Schema Design Review

• Normalization: Appropriate normalization level (avoid over/under-normalization)
• Data Types: Optimal data type choices for storage and performance
• Constraints: Proper use of PRIMARY KEY, FOREIGN KEY, CHECK, NOT NULL
• Default Values: Appropriate default values for columns

🗄️ Database-Specific Best Practices

PostgreSQL

-- Use JSONB for JSON data
CREATE TABLE events (
    id SERIAL PRIMARY KEY,
    data JSONB NOT NULL,
    created_at TIMESTAMPTZ DEFAULT NOW()
);

-- GIN index for JSONB queries
CREATE INDEX idx_events_data ON events USING gin(data);

-- Array types for multi-value columns
CREATE TABLE tags (
    post_id INT,
    tag_names TEXT[]
);

MySQL

-- Use appropriate storage engines
CREATE TABLE sessions (
    id VARCHAR(128) PRIMARY KEY,
    data TEXT,
    expires TIMESTAMP
) ENGINE=InnoDB;

-- Optimize for InnoDB
ALTER TABLE large_table 
ADD INDEX idx_covering (status, created_at, id);

SQL Server

-- Use appropriate data types
CREATE TABLE products (
    id BIGINT IDENTITY(1,1) PRIMARY KEY,
    name NVARCHAR(255) NOT NULL,
    price DECIMAL(10,2) NOT NULL,
    created_at DATETIME2 DEFAULT GETUTCDATE()
);

-- Columnstore indexes for analytics
CREATE COLUMNSTORE INDEX idx_sales_cs ON sales;

Oracle

-- Use sequences for auto-increment
CREATE SEQUENCE user_id_seq START WITH 1 INCREMENT BY 1;

CREATE TABLE users (
    id NUMBER DEFAULT user_id_seq.NEXTVAL PRIMARY KEY,
    name VARCHAR2(255) NOT NULL
);

🧪 Testing & Validation

Data Integrity Checks

-- Verify referential integrity
SELECT o.user_id 
FROM orders o 
LEFT JOIN users u ON o.user_id = u.id 
WHERE u.id IS NULL;

-- Check for data consistency
SELECT COUNT(*) as inconsistent_records
FROM products 
WHERE price < 0 OR stock_quantity < 0;

Performance Testing

• Execution Plans: Review query execution plans
• Load Testing: Test queries with realistic data volumes
• Stress Testing: Verify performance under concurrent load
• Regression Testing: Ensure optimizations don't break functionality

📊 Common Anti-Patterns

N+1 Query Problem

-- ❌ BAD: N+1 queries in application code
for user in users:
    orders = query("SELECT * FROM orders WHERE user_id = ?", user.id)

-- ✅ GOOD: Single optimized query
SELECT u.*, o.*
FROM users u
LEFT JOIN orders o ON u.id = o.user_id;

Overuse of DISTINCT

-- ❌ BAD: DISTINCT masking join issues
SELECT DISTINCT u.name 
FROM users u, orders o 
WHERE u.id = o.user_id;

-- ✅ GOOD: Proper join without DISTINCT
SELECT u.name
FROM users u
INNER JOIN orders o ON u.id = o.user_id
GROUP BY u.name;

Function Misuse in WHERE Clauses

-- ❌ BAD: Functions prevent index usage
SELECT * FROM orders 
WHERE YEAR(order_date) = 2024;

-- ✅ GOOD: Range conditions use indexes
SELECT * FROM orders 
WHERE order_date >= '2024-01-01' 
  AND order_date < '2025-01-01';

📋 SQL Review Checklist

Security

• All user inputs are parameterized
• No dynamic SQL construction with string concatenation
• Appropriate access controls and permissions
• Sensitive data is properly protected
• SQL injection attack vectors are eliminated

Performance

• Indexes exist for frequently queried columns
• No unnecessary SELECT * statements
• JOINs are optimized and use appropriate types
• WHERE clauses are selective and use indexes
• Subqueries are optimized or converted to JOINs

Code Quality

• Consistent naming conventions
• Proper formatting and indentation
• Meaningful comments for complex logic
• Appropriate data types are used
• Error handling is implemented

Schema Design

• Tables are properly normalized
• Constraints enforce data integrity
• Indexes support query patterns
• Foreign key relationships are defined
• Default values are appropriate

🎯 Review Output Format

Issue Template

## [PRIORITY] [CATEGORY]: [Brief Description]

**Location**: [Table/View/Procedure name and line number if applicable]
**Issue**: [Detailed explanation of the problem]
**Security Risk**: [If applicable - injection risk, data exposure, etc.]
**Performance Impact**: [Query cost, execution time impact]
**Recommendation**: [Specific fix with code example]

**Before**:
```sql
-- Problematic SQL

After:

-- Improved SQL

Expected Improvement: [Performance gain, security benefit]

### Summary Assessment
- **Security Score**: [1-10] - SQL injection protection, access controls
- **Performance Score**: [1-10] - Query efficiency, index usage
- **Maintainability Score**: [1-10] - Code quality, documentation
- **Schema Quality Score**: [1-10] - Design patterns, normalization

### Top 3 Priority Actions
1. **[Critical Security Fix]**: Address SQL injection vulnerabilities
2. **[Performance Optimization]**: Add missing indexes or optimize queries
3. **[Code Quality]**: Improve naming conventions and documentation

Focus on providing actionable, database-agnostic recommendations while highlighting platform-specific optimizations and best practices.

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**Source:** [`github/awesome-copilot`](https://github.com/github/awesome-copilot) → `skills/sql-code-review/SKILL.md`