Let us take one ex: Suppose 'XYZ' is customer in Bangalore he was residing in the city from the last 5 years in the period of 5yrs he has made purchases worth of 3 laks. Now he moved to 'HYD'. When u update the 'XYZ' city to 'HYD' in ur Warehouse all the puchases by him will show in city 'HYD' only. This makes warehouse inconsistent. So here CITY is the Critical Column. Solution is use Surrogate Key
Let us take one ex: Suppose 'XYZ' is customer in Bangalore hez residing in the city from the last 5 years in the period of 5yrs he has made purchases worth of 3 laks. Now he moved to 'HYD'. When u update the 'XYZ' city to 'HYD' in ur Warehouse all the puchases by him will show in city 'HYD' only. This makes warehouse inconsistent. So here CITY is the Critical Column.Solution is use Surrogate KeySudheer