SQL Comments

What are SQL Comments?

Comments are notes within your SQL code that the database engine ignores during execution. They help you and your teammates understand the purpose of queries, explain complex logic, and temporarily disable parts of a query.

Syntax

Single-line comment (everything after -- is ignored):

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

Multi-line (block) comment:

/* This is a
   multi-line comment */
SELECT * FROM students;

When to Use

• Explaining why a query uses a specific approach
• Documenting business rules embedded in complex queries
• Temporarily disabling a clause while debugging
• Adding context for future maintainers

Key Points

1. Single-Line — Use -- followed by a space. Everything after it on the same line is a comment.
2. Multi-Line — Wrap text between /* and */. Can span multiple lines.
3. No Nesting — PostgreSQL does not support nested block comments.
4. No Performance Impact — Comments are stripped before execution and have zero runtime cost.
5. Best Practice — Comment complex WHERE conditions, CTEs, and business logic, but avoid over-commenting obvious code.