Support

This index is part of the #__menu table. This table is updated by Joomla®'s core code when an extension is installed or updated. Please keep in mind that during the installation and the update of an extension it is always core Joomla! code managed by the Joomla! project which executes. Us third party extension developers have no say or control over that code, and no option to use something different (the latter on pain of being expelled from the Joomla! Extensions Directory™).

We can try to help Joomla! get its act together.

There is an item on this table with the following attributes:

• menutype: main
• link: index.php?option=com_admintools
• type: component
• client_id: 1

Find it, and delete it.

Then go to System, Manage, Extensions and search for Admin Tools. There will be an extension with its Type set to Package. Select it and click on Uninstall.

If and only if there was no package extension, check if there is an extension with the Type set to Component and its name set to "Admin Tools for Joomla!". Select it and click on Uninstall.

Now retry installing Admin Tools. I believe it should install without further issues.

I do not think that the Joomla support channels will help you any since it's mostly end users, not developers, answering posts in there. It's not even the brightest people. I have seen all sorts of idiotic responses, always blaming third party extension developers for things that are blatantly obvious core Joomla! or hosting issues. 

The message you get from MySQL is very specific. There is a problem with the index idx_client_id_parent_id_alias_language. The values in the index are client_id 1, parent_id 1, alias com_admintools, and language is empty. How do I know? The values of the index are separated by dashes in the error message. Do you have another existing record like that? If you do, delete it.

The other problem might be the name of the index which does not have the table naming prefix of your site's tables. If you have two or more sets of core Joomla! tables in your database, e.g. a second site, tables from an old installation, even bak_ prefixed tables you are likely to have a problem with those old tables and their index (since the name is not unique across Joomla! installations). Does it sound like it's the case?

The correct SQL would be as follows:

ALTER TABLE `#__menu` DROP KEY `idx_client_id_parent_id_alias_language`;
ALTER TABLE `#__menu` ADD UNIQUE KEY `idx_client_id_parent_id_alias_language` (`client_id`,`parent_id`,`alias`(100),`language`);

Replace #__ with the prefix of your tables, including the underscore.

The UNIQUE keyword is important. This is not just a regular index, it's a unique key, meaning that no two rows can have an identical key. This is what was causing us problems to begin with.

If all else fails, let me know. I can make the ticket private, ask you for connection details, and check this myself.