Hi there,
Thank you for your reply.
I'm working on a plugin that I'm planning to release here on wordpress.org, so it's not only for my site.
A simple left join between the users and comments table is really slow with higher number of records, because of the lack of index on the user_id column in the comments table - I tested adding an index to that column on my site and it works really fast.
So, I wanted to ask if adding an index to a default WordPress table would be something that is allowed to be performed in a plugin? I've been concerned that this might not be a good practice either.
Many thanks