I am designing a data warehouse database to be implemented in SQL Server. There are a number of variable length character fields for which I intend to use the varchar field type. On previous data warehouse implementations in Oracle, I frequently set the length for the varchar fields higher than the current data length. I did this so that if the source changes to a longer field in the future, it will not be necessary to update the database. Is there any reason not to do this for a SQL Server database? One example would be, if the actual data field is now up to 10 characters, but I want to make the field type varchar (25) in case the source changes to a larger field in the future. Will this have any negative performance implications?
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