Update Fields On N-side Of 1:n-relation

I have some tables with 1:n-relations. Now I want to update the n-side of the relation. Whatever i do the result is always:

Subquery returned more than 1 value. This is not permitted ...



Both number and internalNumber are unique in table k, which is the 1-side of the relation. Ab is one of the n-side tables.



UPDATE Ab


SET
knr = (select k.internalNumber from Kunden as k where kNumber=k.number)



In my opinion there should be one kNumber at a time and for each
kNumber exists exactly 1 record in k. The following gives the same
result:



UPDATE Ab


SET
knr = k.internalNumber from Kunden as k where kNumber=k.number



Any suggestions? Thanks in advance



Thomas