Hello

To manage the indexes takes also executing time.

Of course, but it seems to be small.

I didn't want to argue against the use of INDEX. I only wants to advice against the creation of indexes for every single column, that is in use for JOINs.

The column user_id was not indexed but, I believe, it is an important and often used column for joining

Yes, you are right without a doubt.

- why this column is not set as FOREIGN KEY?

At the time, when Alex defined the table structure of mlf (mlf1, the structure for mlf2 based on that), he and also no one else of us was aware of FOREIGN KEYS to tie the tables to each other and other the abilities of a MySQL-server (that evolved a lot since then). So this feature was never implemented in mlf.

The first column, that came in my mind while reading this thread is the column category of the entries table.

This column is set as key e.g.

KEY category (category)

. Isn't it similar to an INDEX?

Yes, it is and yes, it is.

Tschö, Auge