Like the user's mobile phone number, city of residence scene will change these dimensions, the user dimension tables which will affect the data, this situation is called a slowly changing dimension. 1 . Need to track the latest changes, updates the data for the latest 2 . Need to keep historical data, it can be the primary key to dwid add a column corresponding data rms (identification start and expiration time) 3. dimension requires relatively few words, you can directly increase the dimension corresponding to the history of columns (for the dimension value and less variation)