Import or Directy query with about a billion data

Hi changhai ,

For your first question, we think using Import Mode might reach limitation of dataset (For example 1,999,999,997 limit on the number of distinct values that can be stored in a column and 1-GB limit for datasets stored in Shared capacities). And If your first table will update frequently, it might take much time in scheduled refresh because of the large dataset. The most important thing is, although DirectQuery Mode has some limitation in tranforming data and DAX, but we can easily change dataset from DirectQuery to Import. Consider your large dataset, we suggest you to try the DirectQuery Mode first, if it cannot meet your requirement, you can change it to Import Mode. 

For the second question, When using Import Mode, the data will be refresh and stored in the model, we can execute the on-demand refresh or set the scheduled refresh to make it up-to-date in service and do not need to re-publish again.

For the last question, Use of DirectQuery does have potentially negative implications, as detailed in this section. Some of those limitations are slightly different depending upon the exact source that is being used. Please refer to this document about the Implications of using DirectQuery. The implication of Import mode mostly is the limitation on size of dataset and the refresh time if your dataset is large, also it will take much more menory while refresh.

Best regards,