💬 SQL COMMENTS – Write Clear and Maintainable SQL Code
🧲 Introduction – Why Use Comments in SQL?
SQL comments allow you to annotate your queries and scripts with helpful explanations, descriptions, or reminders. They improve readability, maintainability, and team collaboration.
🎯 In this guide, you’ll learn:
- Syntax for single-line and multi-line comments
- Platform-specific behavior
- Best practices for writing clean and meaningful comments
🗒️ 1. Single-Line Comments
-- This is a single-line comment
SELECT * FROM users; -- Get all user records
✅ Use -- to mark a comment until the end of the line.
📄 2. Multi-Line Comments
/*
This is a multi-line comment.
It can span multiple lines of explanation.
*/
SELECT * FROM orders;
✅ Use /* */ to wrap multiple lines of comment.
⚙️ 3. Database-Specific Notes
| Database | Single-Line | Multi-Line |
|---|---|---|
| MySQL | --, # | /* */ |
| PostgreSQL | -- | /* */ |
| SQL Server | -- | /* */ |
| Oracle | -- | /* */ |
✅ Most systems support both styles. # is MySQL-only.
🔍 4. Comment Use Cases
| Scenario | Example |
|---|---|
| Disable a query temporarily | -- SELECT * FROM logs; |
| Describe logic or joins | -- Joining orders with customers |
| Label sections of a script | /* Step 1: Load staging data */ |
| Clarify filter conditions | -- Exclude inactive users from the result |
📘 Best Practices
| ✅ Recommended | ❌ Avoid This |
|---|---|
| Use comments to explain why, not just what | Leaving code without context |
| Update comments as queries evolve | Letting them become misleading |
| Keep comments brief and relevant | Writing essays in SQL comments |
📌 Summary – Recap & Next Steps
SQL comments are essential for code quality, collaboration, and long-term maintenance. They guide developers, clarify purpose, and help avoid confusion.
🔍 Key Takeaways:
- Use
--for single-line and/* */for block comments - Supported by all major RDBMS with minor variations
- Use comments to improve code readability and manage complex logic
⚙️ Real-World Relevance:
Used in schema scripts, stored procedures, analytics reports, and CI/CD SQL deployments.
❓ FAQ – SQL Comments
❓ Can I comment out part of a SQL query?
✅ Yes. You can disable code using -- or /* ... */.
❓ Are comments stored in the database?
❌ No. They’re ignored during parsing and not stored in the execution plan.
❓ Can comments cause SQL errors?
✅ Rarely. Only if used inside strings or misplaced syntax.
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