SQL SERVER – Two Different Ways to Comment Code – Explanation and Example

SQL Server has two different ways to comment code. You may connect here.

Commenting in SQL Server: Two Approaches

Comments are essential in SQL Server for improving code readability, maintaining documentation, and sharing insights about specific code blocks. SQL Server supports two primary ways to add comments: line comments and block comments. Let’s explore both in detail:

1) Line comments

Line comments begin with two dashes (--) and continue until the end of the line. Anything after the two dashes on the same line is treated as a comment and will not execute. This type of comment is ideal for short notes or clarifications within your SQL code. It can be used anywhere—on its own line or after a line of code.

Example:

SELECT *
FROM Sales.Products -- This table contains product information
WHERE ProductID > 10 -- Filters for products with an ID greater than 10

In the example above, the comments explain what the code is doing without interfering with execution. Everything before the -- runs as normal T-SQL code.

2) Block comments 

Block comments are more versatile and suitable for longer explanations or detailed documentation. They begin with /* and end with */. Everything within these markers is treated as a comment, and it can span multiple lines. This makes block comments particularly useful for temporarily disabling large sections of code or for providing detailed information about the logic.

/* This query retrieves all products from the Sales.Products table
   and filters the results to include only products with an ID
   greater than 10. */
SELECT *
FROM Sales.Products
WHERE ProductID > 10

Block comments can also be nested, making them useful when working with complex scripts. However, it’s important to note that the GO command is not allowed within comments, as it signals a batch separator and is processed by the SQL Server Management Studio (SSMS).

Additional Notes on Comments

1. No Length Limit: SQL Server imposes no limit on the length of comments, making them a flexible tool for documentation.
2. Nesting Allowed: Comments can be nested, which helps when disabling a portion of the code that already contains comments.
3. Best Practices: Use comments thoughtfully to explain complex logic, assumptions, or decisions in your code.

By combining line and block comments effectively, you can make your SQL scripts more understandable and maintainable, benefiting your team and future development efforts.

Reference: Pinal Dave (https://blog.sqlauthority.com)