{"id":5716,"date":"2017-02-15T01:20:47","date_gmt":"2017-02-15T08:20:47","guid":{"rendered":"http:\/\/www.mysqltutorial.org\/?page_id=5716"},"modified":"2023-12-29T05:47:12","modified_gmt":"2023-12-29T12:47:12","slug":"mysql-comment","status":"publish","type":"page","link":"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-comment\/","title":{"rendered":"MySQL Comments"},"content":{"rendered":"
\n
\"MySQL<\/figure>\n<\/div>\n\n\n

Summary<\/strong>: in this tutorial, you will learn how to use MySQL comments to document your code in MySQL.<\/p>\n\n\n\n

MySQL comments are essential for documenting your database schema, SQL queries, and stored procedures<\/a>.<\/p>\n\n\n\n

They help you and other developers understand the code and its purpose. <\/p>\n\n\n\n

1) Single-Line Comments<\/h2>\n\n\n\n

Single-line comments are used to add comments on a single line.<\/p>\n\n\n\n

MySQL supports two types of single-line comments:<\/p>\n\n\n\n

Using --<\/h3>\n\n\n\n

You can add a single-line comment using two hyphens (--<\/code>) followed by your comment text. Any text following --<\/code> on the same line is treated as a comment. For example:<\/p>\n\n\n

-- This is a single-line comment\r\nSELECT * FROM employees;<\/code><\/span><\/pre>\n\n\n
Using #<\/h3>\n\n\n\n
Alternatively, you can use the hash (#<\/code>) symbol to add single-line comments. Any text following #<\/code> on the same line is treated as a comment. For example:<\/p>\n\n\n
# This is another single-line comment<\/span>\r\nSELECT * FROM customers;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
2) Multi-Line Comments<\/h2>\n\n\n\n
Multi-line comments allow you to add comments spanning multiple lines. MySQL supports two types of multi-line comments:<\/p>\n\n\n\n
Delimited by \/* ... *\/<\/h3>\n\n\n\n
You can enclose your comments within \/*<\/code> and *\/<\/code> to create multi-line comments. Everything between the opening \/*<\/code> and closing *\/<\/code> is treated as a comment. For example:<\/p>\n\n\n
\/* This is a\n   multi-line comment *\/<\/span>\nSELECT * FROM orders;<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Using -- for Multi-Line Comments<\/h3>\n\n\n\n
While --<\/code> is primarily for single-line comments, you can use it for multi-line comments by adding --<\/code> at the beginning of each line. For example:<\/p>\n\n\n
-- This is a multi-line comment\r\n-- that spans multiple lines\r\nSELECT * FROM products;<\/code><\/span><\/pre>\n\n\n
3) Executable comments<\/h2>\n\n\n\n
In MySQL, executable comments support portability between different databases. These comments allow you to embed SQL code that will execute only in MySQL but not in other databases.<\/p>\n\n\n\n
The following illustrates the executable comment syntax:<\/p>\n\n\n
\/*! MySQL-specific code *\/<\/span><\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\n\n\n
For example, the following statement uses an executable comment:<\/p>\n\n\n
SELECT<\/span> 1<\/span> \/*! +1 *\/<\/span><\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\n\n\n
The statement returns 2 instead of 1. However, it will return 1 if you execute it in other database systems.<\/p>\n\n\n\n
If you want to execute a comment from a specific version of MySQL, you use the following syntax:<\/p>\n\n\n
\/*!##### MySQL-specific code *\/<\/span><\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\n\n\n
The string ‘#####’ represents the minimum version of MySQL that can execute the comment. The first # is the major version e.g., 5 or 8. The second 2 numbers (##) are the minor version. And the last 2 is the patch level.<\/p>\n\n\n\n
For example, the following comment is only executable in MySQL 5.1.10 or later:<\/p>\n\n\n
CREATE<\/span> TABLE<\/span> t1 (\n    k INT<\/span> AUTO_INCREMENT,\n    KEY<\/span> (k)\n)  \/*!50110 KEY_BLOCK_SIZE=1024; *\/<\/span><\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
    \n
  • Use comments to document your SQL statements, schemas, and stored procedures.<\/li>\n<\/ul>\n
    \n\t
    \n\t\t
    Was this tutorial helpful? <\/div>\n\t\t
    \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
    \n\t\t
    \n\t\t\t
    <\/div>\n\t\t\t\n\t\t\t