[eight part essay] what is the difference between unrepeatable reading and unreal reading?

such as , A piece of data in the database , Zhang San =18 year , Once this data is read by the transaction for the first time , Every subsequent reading is Zhang San =18 year , The value of the data is impossible to change , This is it. It can't be read repeatedly . But if Zhang San is found in the next reading =18 The number of years old is missing （ Or other data ）, Like an illusion , This is it. Fantasy reading .
It can't be read repeatedly ： The value embodied in a certain line .
Fantasy reading ： Reflected in the number of rows .