In SQL, comments are used to add explanatory notes or remarks within the SQL code. Comments are ignored by the database engine and are meant for developers and administrators to document and clarify the purpose or functionality of the code. There are two types of comments commonly used in SQL:
- Single-line comments: Single-line comments begin with two consecutive hyphens (–). Anything written after the double hyphens is considered a comment and is ignored by the database engine. For example:
SELECT * FROM customers; -- This is a comment
- Multi-line comments: Multi-line comments are used to add comments that span across multiple lines. They start with /* and end with */. Any text between these delimiters is treated as a comment. For example:
/* This is a multi-line comment that can span across multiple lines. */ SELECT * FROM orders;
It’s good practice to use comments in your SQL code to make it more understandable and maintainable, especially when working on complex queries or stored procedures. Comments can provide context, explain the purpose of certain sections, or indicate important details for future reference.