Android SQLite - Update table only if different

I currently successfully use a SQLite database which is populated with data from the web. I create an array of values and add these as a row to the database.

Currently to update the database, on starting the activity I clear the database and repopulate it using the data from the web.

Is there an easy method to do one of the following?

A: Only update a row in the table if data has changed (I'm not sure how I could do this unless there was a consistent primary key - what would happen is a new row would be added with the changed data, however there would be no way to know which of the old rows to remove)

B: get all of the rows of data from the web, then empty and fill the database in one go rather than after getting each row

I hope this makes sense. I can provide my code but I don't think it's especially useful for this exam开发者_StackOverflowple.

Context:

On starting the activity, the database is scanned to retrieve values for a different task. However, this takes longer than it needs to because the database is emptied and refilled slowly. Therefore the task can only complete when the database is fully repopulated.

In an ideal world, the database would be scanned and values used for the task, and that database would only be replaced when the complete set of updated data is available.

Your main concern with approach (b) - clearing out all data and slowly repopulating - seems to be that any query between the empty and completion of the refill would need to be refused.

You could simply put the empty/repopulate process in a transaction. Thereby the database will always have data to offer for reading.

Alternatively, if that's not a viable solution, how about appending newer results to the existing ones, but inserted as with an 'active' key set to 0. Then, once the process of adding entries is complete, use a transaction to find and remove currently active entries, and (in the same transaction) update the inactive entries to active.