SQL Comments -A Complete guide

SQL comments are annotations within the SQL code that are ignored by the database engine during execution. They serve as explanatory notes or reminders for developers and are not processed as part of the SQL query. Comments are a crucial tool for documenting code, providing insights into the logic and purpose behind each line or block of code.

In the below PDF we discuss about SQL Comments in detail in simple language, Hope this will help in better understanding.

SQL Tutorial

Types of SQL Comments:

SQL comments can be divided into two types:

1.  Single-Line Comments:

The most basic form of SQL comment is the single-line comment. In SQL, a line beginning with two consecutive hyphens (–), known as a double-dash, is treated as a comment. For example:

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

Single-line comments are handy for adding brief explanations to specific lines of code, making it easier for developers to understand the purpose or context of a particular query.

2. Multi-Line Comments:

In addition to single-line comments, SQL also supports multi-line comments. These are enclosed within /* and */, allowing developers to add more extensive comments spanning multiple lines. Multi-line comments are particularly useful for documenting complex queries or providing detailed explanations. Here’s an example:

This is a multi-line comment
that provides additional information
about the purpose of the SQL query.
SELECT column1, column2
FROM orders
WHERE order_date > '2023-01-01';

Using multi-line comments, developers can offer comprehensive insights into the logic and rationale behind a series of SQL statements.

Benefits of SQL Comments:

  • Code Documentation: SQL comments play a vital role in documenting code. They help developers understand the intention behind each query, making it easier to maintain and troubleshoot the code in the future.
  • Collaboration: When working on projects with multiple developers, SQL comments become a communication tool. They enable team members to share information about the code, reducing the learning curve for those who may not be familiar with a particular part of the database schema or query logic.
  • Debugging: Comments can be invaluable during the debugging process. When an issue arises, well-documented SQL code can expedite the identification of problems and facilitate quicker resolutions.
  • Code Review: During code reviews, comments offer reviewers insights into the thought process of the original developer. This aids in identifying potential improvements, ensuring that the code adheres to best practices, and promoting overall code quality.

Related Question

An SQL comment is a way to include explanatory or descriptive text in SQL code that is not executed as part of the query. Comments help improve code readability and provide information to developers.

In SQL, you can add a single-line comment by using the double hyphen (–). Everything following the double hyphen on that line is treated as a comment and is not executed.


No, it is not necessary to remove comments before executing SQL code. Comments are ignored by the database engine during execution. However, removing unnecessary comments in production code can slightly improve performance and reduce code size.

Comments can be strategically placed in SQL code to temporarily disable or isolate portions of code for debugging purposes. This allows developers to test different parts of the code without removing or altering the original logic

A primary key is a unique identifier for a record in a table. It ensures that each row in a table can be uniquely identified and helps establish relationships between tables. A primary key column cannot contain null values, and there can be only one primary key in a table.


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