Improve table structures for metadata as central point of SQL queries

[petr-kus]

We use a lot of metadata in the Robot Framework. The problem is that the structure of the tables around metadata doesn't count with this.

When we want to filter according to some metadata we have to look at the table, filter make many joins... etc. The SQL queries are too difficult in these cases.

Maybe that would help us design it differently or add columns.

I see there is a weak point in the design of the database. Is there a possibility to improve?