Need Calendar Month to be a key

[sra2786]

I am very new to Access. I need to include Calendar Month (ie, 201710, 201711) as part of a key in a table. There will be two key fields (Calendar Month + State) that make up the key for this table. The rates will change each month and that is why Calendar Month needs to be part of the key.



Table Examples Format
Calendar Month 201710, 201711 Text or Number
State OH, KY Text
Rate 1.00, 1.32 Currency

Questions
1. Should I make Calendar Month a text or numeric field. The Calendar Month will be used to link to data in another table
2. Is it required to add an "Id" (Autonumber) field

Thanks.

[June7]

If rates will change each month then month and state are not enough for a unique identifier, assuming data will be multi year. Autonumber field is not required, however this could the PK that is saved as FK to related table then set Year, Month, State as compound index to prevent duplicate combinations.

[CJ_London]

you should keep the two fields separate - and each indexed separately. Any query would then the be filtered on the basis of

yearmonth=12345 and state='OH'

also store the yearmonth as a numbers use fewer bytes than text so take up less space so indexing will be faster.

Also means if you want to filter on state then you do not have to split your index - which will be significantly slower with an sort of data volumes.

I would have a separate ID as autonumber, it is just good practice. If you want to prevent duplicates, you can still set a multi field index on the two fields