Comments

Introduction

For various reasons, it can be useful to add comments to code.

For example:

• For clarification of the code.
• To indicate what still needs to be done.

Below we see a first example of a comment

SELECT
  -- Select all columns
  *
FROM
  movies
WHERE
  year > 2000
ORDER BY
  rank DESC;

---

1. Line comments

When you want to place comments in 1 line, use a line comment.

For this, use two dashes:

-- <comment>

See the example below:

SELECT
  -- This is a line comment
  *
FROM
  movies
WHERE
  year > 2000
ORDER BY
  rank DESC;

---

2. Block comments

When you want to place comments in multiple lines, use a block comment.

For this, use /* to open, and */ to close:

/*
This is a block comment.
It allows comments in multiple lines.
Indeed, multiple lines.
*/

See the example below:

/*
Author:         SQL training
Creation date:  Not so long ago 
Description:    Select data from movies table starting at year 2000
*/
SELECT
  *
FROM
  movies
WHERE
  year > 2000
ORDER BY
  rank DESC;

---

Summary

• With comments, you can add commentary to code.
• Line comments on one line:

  -- This is a line comment
  

• Block comments on multiple lines:

  /*
  This is a block comment.
  It allows comments in multiple lines.
  Indeed, multiple lines.
  */