Why Do MySQL Dumps Contain Mysterious Comments, and Should I Remove Them?

Resolving Mysterious Comments in MySQL Dumps

When attempting to create a structure-only dump of a MySQL database using mysqldump, you may encounter unexpected comments that persist despite your attempts to eliminate them. These comments are not actually comments; they are conditional-execution tokens used by MySQL to control the execution of specific statements based on the version of the server.

The conditional-execution syntax can be confusing at first glance, but it serves an important role in ensuring that certain operations are only performed if the server version is high enough to support them. For instance, the line:

/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;

indicates that the statement will only be executed if the MySQL server version is 4.00.14 or higher. This ensures that the statement does not cause errors on older versions of MySQL.

It's important to retain these conditional-execution tokens in your database dump because they ensure that the dump can be successfully imported into servers of different versions. Attempting to remove them can result in errors or unexpected behavior when importing the dump.

However, if you wish to preserve other genuine comments, such as MySQL dump version information, while still excluding the conditional-execution tokens, you can use a combination of regular expressions and text processing tools to selectively filter out the undesired tokens.

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