How to Comment in MySQL

In MySQL, a comment is a text that is added to the SQL code to provide extra information about the code. Comments are not executed in MySQL; instead, comments are ignored by the MySQL server. They are like documentation inside the code, which makes it simple for developers to understand the logic behind the SQL statements.

Types of comments in MySQL:

There are two kinds of comments in MySQL, which are as follows:

Single-Line Comments:

Single-line comments begin with a double hyphen (--) or hash symbol (#). They allow you to add notes in a row. Anything written after a double hyphen on the same line is a comment and is not executed by the MySQL server.

Multi-Line Comments:

Multi-line comments are enclosed between /* and */ characters. They can span multiple lines, which is beneficial for long explanations or inefficient code sections. Anything between the /* and */ characters will be treated as a comment, which is not executed.

Need to use comments in MySQL:

• Well-placed comments increase the readability of your SQL code. Comments help break down complex queries or procedures into understandable parts, which makes it easier to follow the logic behind the code. Clear and concise comments act as guideposts, which make sure that the purpose of the code is clear to anyone reviewing it.
• Comments facilitate effective collaboration between team members. If you add comments to your SQL code, it enables better communication about the code's purpose, behavior, and assumptions made during development. It helps team members work together more efficiently.
• Comments play an important role during code maintenance and debugging. Comments can help to identify and resolve problems more quickly.
• When testing SQL queries, comments can be used to disable or exclude specific parts of the code temporarily. By commenting on parts of the code, you can isolate and focus on individual sections to facilitate the testing and optimization process.
• Comments provide a record of changes made, explaining the reasons behind certain modifications or documenting the thought process at the time of development which is valuable when revisiting code after a period of time or when onboarding new team members.
• Comments can be used to explain specific parts of code and provide valuable insight to other developers or your future self, helping them to understand the logic behind the optimizations and improve upon them.
• Comments can be used to document the business logic or rules embedded in the SQL code. It helps capture and explain the decision-making processes used to generate query results.
• Comments provide insights into the business logic and make the code more transparent and support knowledge transfer among developers.
• Comments can be used to describe the mapping rules, data manipulation steps, or any transformations performed on the data. It provides clarity and context to the data pipeline, which makes it easier to understand and troubleshoot the transformations.
• When encountering issues or bugs in the code, comments can be used to document the troubleshooting steps taken, potential solutions, or explanations for the cause of the problem. It helps diagnose and resolve issues more efficiently, especially when revisiting the code later or when multiple developers are involved in troubleshooting.

Examples of single-line comments in MySQL:

The syntax for using the hash symbol (#):

Example:

By using the above command, we will get the records from the 'electrical_appliances' table. As you can see below, the MySQL statement has been executed, and the MySQL server ignores the comment during execution.

The syntax for using the double hyphen (--):

Example:

DESC electrical_appliances; --This statement will describe the 'electrical_appliances' table

The above SQL statement is used to describe the 'electrical_appliances' table. As you can see below, the table has been described, and the MySQL server ignores the comment during execution.

Examples of multi-line comments in MySQL:

Syntax:

Example:

The above SQL command will retrieve records from the 'students' table. As you can see below, the SQL statement is executed, and the MySQL server ignores the comment during execution.

Conclusion:

In this article, you have understood how to comment in MySQL. Comments are used to describe statements that are helpful for future use or new team members' use. You can comment in MySQL in two ways: single-line comment using the hash symbol (#) or double hyphen (--) and multi-line comment using /* and */ characters.