SQLite syncing with remote data to act as local data

There is a need to get a set of data from a remote server and distribute to a group of local computers. The data must not be deleted then inserted. The data also may not be available on remote server due to it being closed and removed.

If the data cannot be deleted (truncated) then the only way is to do "insert or ignore" so that existing data is either updated if it exists or inserted if it is not. Meanwhile, there is a problem of remote data does not exist while local data exists.

Well, it is quite easy. Two tables are used. One for the main table with a key index field and the other one only the key index field. Both table index uses the same field.

When importing data, both tables are inserted with the remote data. The second table was truncated before the import starts. This means the main table contains new and old data while the second table only contains the new data. At the end of importing, just simply delete from the main table where the index field not exists in second table. Thus only the imported data remains in the main table.

Example of the "insert or ignore" goes like this

Insert or ignore on maintable (f1, f2,f3....) values ('x1', 'x2, 'x3'...);update maintable set f2='x2', f3='x3' where f1='x1'

It seems that the above will insert and then update if the index is not found but it is still better than using two sql statements to insert or update plus one statement to check whether the index exists before doing either insert or update statement.

Example of the delete command goes like this

delete from maintable where  f1 not in (select f1 from secondtable)

The main table can then be access by local users.