A user in database a has execute permission on a stored procedurte in database a, that stored procedure reads table 1 in database b however when the user executes that procedure they get the following message.

The SELECT permission was denied on the object '1', database 'b', schema 'dbo'.

If I give the user db_datareader permission in database b then the procedure works.

I didn't think I needed to do that though. Please can somebody explain how wrong I am!