SQL Comments

Overview

Comments are annotations in SQL code that are not executed as part of the SQL statement. They are used to provide explanations or notes about the code, making it easier to understand and maintain.

Types of SQL Comments

• Single-Line Comments: Used for brief comments that occupy a single line.
• Multi-Line Comments: Used for longer comments that may span multiple lines.

Single-Line Comments

Single-line comments can be created using two hyphens (--) or the /* syntax. Everything following these symbols on the same line is treated as a comment.

-- This is a single-line comment
SELECT * FROM Employees;  -- This selects all employees

Multi-Line Comments

Multi-line comments start with /* and end with */. They can span multiple lines and are useful for longer explanations.

/* This is a multi-line comment
   that can span multiple lines.
   It is useful for detailed explanations. */
SELECT * FROM Departments;

Usage Examples

Here are a few practical examples of using comments in SQL:

Example 1: Using Single-Line Comments

-- Get the total number of employees
SELECT COUNT(*) FROM Employees;

Example 2: Using Multi-Line Comments

/*
   This query retrieves the names of all employees
   in the Sales department.
*/
SELECT Name FROM Employees WHERE Department = 'Sales';

Best Practices for Using Comments

• Use comments to explain complex logic or important decisions in your SQL code.
• Avoid redundant comments that state the obvious. Keep comments concise and relevant.
• Regularly update comments to reflect any changes in the code or logic.

Conclusion

Comments are an essential part of writing maintainable SQL code. They help document your code and make it easier for others (or yourself) to understand it in the future. Properly using comments can significantly improve the readability and maintainability of your SQL scripts.