MySQL conditional comments are enclosed within `/*! ... */` and can include a version number to specify the minimum version of MySQL that should execute the contained code. The code inside this comment will be executed only if the MySQL version is greater than or equal to the number immediately following the `/*!`. If the MySQL version is less than the specified number, the code inside the comment will be ignored. * `/*!12345UNION*/`: This means that the word UNION will be executed as part of the SQL statement if the MySQL version is 12.345 or higher. * `/*!31337SELECT*/`: Similarly, the word SELECT will be executed if the MySQL version is 31.337 or higher. **Examples**: `/*!12345UNION*/`, `/*!31337SELECT*/`
Source: SQL Injection/MySQL Injection.md in PayloadsAllTheThings. From PayloadsAllTheThings by Swissky and contributors. MIT License, Copyright (c) 2019 Swissky.