>>Looks like you DO need both fields in your join condition. You also have to >make sure that your WHERE condition matches EXACTLY the index expression. So, >it either should be index on YEAR(verw_mut) tag YEAR_DATE or simple index on >date, but then you should use date range instead of years.
>
>Okay,I'll double check tomorrow at work. Maybe I did something wrong, I indexed by hand: so opening database, the table, modifying the properties and adding an index. I assumed that this is the same as :

index on year(verw_mut tag Year_Date

. Or is there a difference?

No difference. Doing it from the table designer is the same as using INDEX command.