When you import data from an external source, Access 2007 often has to use default data types or lengths that can accommodate all the incoming data. You will then need to correct these default settings for your needs. For example, Access assigns a maximum length of 255 characters to text data imported from a spreadsheet or a text file. Even when the source of the data is another database, Access might choose numeric data types that can accept the data but that might not be correct. For example, numeric data in dBASE might be of the Integer type, but Access stores all numeric data from dBASE with a Field Size setting of Double.
Unless you’re importing data from an SQL or Paradox database that has a primary key defined, Access does not define a primary key in the new table, so you must do that yourself. Also, if you did not include field names when importing a text or spreadsheet file, you’ll probably want to enter meaningful names in the resulting table.