><snip>
>>Note that "special" is a field, not the index. In other words, it doesn't ? > >matter if Table1 is indexed or not.
>
>Do you mean, I can set a relation without indexing if it's a field, I didn't know hat?

Yes. Basically, the SET RELATION is always:

from an expression - usually, this will be a field. But never an index. Of course, you may happen to have an index by the same name as a field - but this is not relevant. The "from" table can be unsorted, or ordered by any index. This will affect the sorting order, but not the relation.

into a table. The table must (usually) have an active index that matches the expression which I mentioned in the previous paragraph.

Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)