MySQL Comments: Definition, Syntax, and Examples

In MySQL, comments are used to add notes or explanations within your SQL code. Comments are ignored by the database engine and are solely for developers to make the code easier to read and understand.

Types of Comments in MySQL

MySQL supports three types of comments:

Single-line Comments using --
Single-line Comments using #
Multi-line Comments using /* ... */

Single Line Comments

Use -- (two hyphens) followed by a space for a single-line comment.
It is often used for in-line documentation.

Example

-- This query selects all students

SELECT * FROM students;

SELECT name, age -- Fetching only name and age

FROM students;

Try it yourself

Single-line Comments Using `#`

# is another way to add single-line comments in MySQL.
This style is common in MySQL scripts.

Example

# Select students who scored above 80

SELECT * FROM students WHERE score > 80;

Try it yourself

Note

# comments are not part of the SQL standard, but they work in MySQL.

Multi-line Comments

Use /* to start the comment and */ to end it.
Suitable for large comments or when commenting out blocks of SQL code.

Example

This query selects the student name and score

from the students table where the score is above 75.

SELECT name, score

FROM students

WHERE score > 75;

Try it yourself

Example - Commenting Out a Block of Code

SELECT name FROM students;

SELECT age FROM students;

SELECT name, age FROM students;

Try it yourself

When to Use Comments

To explain the purpose of a query.
To add notes about changes or updates.
To temporarily disable parts of a query for debugging.
To describe complex joins, subqueries, or calculations.

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MySQL Comments

Types of Comments in MySQL

Single Line Comments

Single-line Comments Using #

Multi-line Comments

When to Use Comments

Single-line Comments Using `#`