How to Use Comments in SQL

Introduction to Comments in SQL

Comments in SQL are one of the fundamental needs when writing complex queries. But why should we use comments? Simply put, commenting allows us to add additional explanations and guidelines to our SQL code, which helps make it easier for others to read and understand the code.

Comments can serve as reminders for us while executing our tasks. For example, consider a code you write that requires deep understanding of certain tables and their relationships. Commenting in such scenarios can help ensure your thoughts remain fresh in the code for that specific moment, reducing the need to review everything from scratch.

Moreover, when others work on your project, comments can act as guides that aid in navigating large databases. Particularly in larger projects or teams, the importance of this subject cannot be overstated.

Unlike many programming languages, SQL has simple methods for adding comments that make it easy to utilize them. In SQL, there are two types of comments: single-line and multi-line.

Using Single-Line Comments

Single-line comments start with two dashes (--). This type of comment remains until the end of the current line.

Using Multi-Line Comments

For multi-line comments, we can use /* to start the comment and */ to end it. These comments can span multiple lines and allow us to add longer explanations.

-- this is a single-line comment
SELECT * FROM Users; -- this query returns all users

/* this is a multi-line comment
   that can extend over several lines
   giving more detail. */
SELECT Name, Email FROM Users;

Line-by-Line Explanations

-- this is a single-line comment
This single-line comment is simply there to provide context for what follows.

SELECT * FROM Users; -- this query returns all users
This SQL command selects all the records from the Users table, with a brief comment at the end for clarification.

/* this is a multi-line comment ...
This line starts a multi-line comment that can provide comprehensive explanations.

SELECT Name, Email FROM Users;
This query selects only the name and email of users, with a separate comment illustrating the usage of comments in SQL.