Im not sure if i understand your question,
but you can't use SQL JOIN on two (or more) databases. You can only JOIN Tables of the same database. If you really want to JOIN databases, then you have to do that by hand
i.e. query a list of records from database1.tableA , query list of records from database2.tableB, then save them in a hashmap with the join condition as key and join them and save the join result
Update:
Ok, so if you want to add records from "newDatabase" (provided to you) to the "usersDatatbase" (the current database of the user of your app) with an app update you simply have to versioning the database. Every database in android has a version and you can react on version changes in SQLiteOpenHelper onUpgrade(). Usually you would use this method to alter the table schema, but I think it's completely ok for what you are going to do. So let's assume you have released you app to the playstore with final int DATABASE_VERSION = 1. After some weeks you decide to update the database. So what you have to do is set final int DATABASE_VERSION = 2 (sets database version to 2) and release the new update to the playstore. If the user of your app installs your update from playstore (with database version == 2) onUpgrade() will be called, where you check the old version of the database and the new version and do the data migration (i.e. rename the names with the new provided ones). After a month you want to update the database to final int DATABASE_VERSION = 3 and so on. I hope you get the point. The only thing you have to keep in mind is, that a user can skip an playstore update of your app. For instance a user with app version 1 have not updated to version 2 but directly upgrades from version 1 to 3. In that case you may (depends on your database changes you want to apply) have to migrate from the database from 1 to 2 and then from 2 to 3.
Example:
public class MySQLiteHelper extends SQLiteOpenHelper {
public static final String TABLE_COMMENTS = "comments"; public static final String COLUMN_ID = "_id"; public static final String COLUMN_COMMENT = "comment";
private static final String DATABASE_NAME = "commments.db"; private static final int DATABASE_VERSION = 3;
// Database creation sql statement private static final String DATABASE_CREATE = "create table "
+ TABLE_COMMENTS + "(" + COLUMN_ID
+ " integer primary key autoincrement, " + COLUMN_COMMENT
+ " text not null);";
public MySQLiteHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION); }
@Override
public void onCreate(SQLiteDatabase database) {
database.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (newVersion == 2){
migrateFrom1To2(db);
}
if (newVersion == 3){
if (oldVersion == 1){
migrateFrom1To2(db);
migrateFrom2To3(db);
} else {
// oldversion == 2
migrateFrom2To3(db);
}
}
}
private void migrateFrom1to2(SQLiteDatabase db){
// TODO insert the new data into the users local database
}
private void migrateFrom2To3(SQLiteDatabase db){
// TODO insert the new data into the users local database
}
}
