How to define combination of fields as a non duplicate combination.

I have a table with some fields. Two of them are Nr (string) and Anno (integer). Each of these two may exist as duplicates, but the combination of any two may only exist once. Is there a way to define the table to ensure that?
(The reason is that Nr refers to a customer and Anno refers to a year and each customer may only occur once each year.)
SShot of table design
Fritz PaulAsked:
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crystal (strive4peace) - Microsoft MVP, AccessRemote Training and ProgrammingCommented:
Make a Unique Index on multiple fields:

1. go to the Design view of the table
2. make a unique index on the first field
-- click on the field
-- set Indexed in bottom pane to Yes (No Duplicates)
3. open the indexes window (lightening bolt icon on the Design ribbon)
4. in the second column, the field column, add a second field to the same index by filling out the next row.
 - The first column of the next row will be blank
5. if necessary, add a third field the same way

If you want some of the fields in the index to be allowed to not be filled out then set Ignore Nulls to Yes (in addition to Unique is Yes) in the properties in the Indexes window -- this way, the combination will only be tested if all fields have values.

if you need more explanation for any of the instructions, please ask

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Fritz PaulAuthor Commented:
Thanks. That was so quick and sooo helpful
crystal (strive4peace) - Microsoft MVP, AccessRemote Training and ProgrammingCommented:
you're welcome ~ happy to help
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