遍历SQLite表的行以更新ID

Question

I'm working on an Android app with an SQLite database.

I have a table called REMINDER (with 2 columns: REMINDER_ID and REMINDER_VALUE) and I am allowing the user to delete any record from that table. For reasons that would take a bit to explain, I need the REMINDER_ID column to always have sequential numbers. So, if the user deletes row 2, I need to eliminate that gap, so row 3 becomes row 2, row 4 becomes row 3, etc..

I wrote a method in my DBHelper class to do the update of the db whenever a row is deleted, but I'm not sure whether this is the best way to do it.

Below is the method to delete a row from the REMINDER table. As you can see, before I delete the row, I check whether it's the last row or not, because if it is I don't have to bother updating the ids.

public void deleteReminder(int reminder_id){
    SQLiteDatabase db = this.getWritableDatabase();

    String selectQuery = "SELECT MAX(" + COLUMN_REMINDER_ID + ") FROM " + REMINDERS_TABLE;
    Cursor cursor = db.rawQuery(selectQuery, null);
    int maxId = cursor.getInt(cursor.getColumnIndex(COLUMN_REMINDER_ID));

    db.delete(REMINDERS_TABLE, COLUMN_REMINDER_ID + "= ?", new String[] {String.valueOf(reminder_id)});

    if (reminder_id != maxId){
        updateRemindersIds();
    }

    cursor.close();
    db.close();
}

This is the method used for updating the id's:

    public void updateRemindersIds(){

        SQLiteDatabase db = this.getWritableDatabase();
        String selectQuery = "SELECT * FROM " + REMINDERS_TABLE;
        Cursor cursor = db.rawQuery(selectQuery, null);
        ContentValues values = new ContentValues();
        int new_id = 1;

        if(cursor.moveToFirst()){
            do{
                values.put(COLUMN_REMINDER_ID, new_id);
                int old_id = cursor.getInt(cursor.getColumnIndex(COLUMN_REMINDER_ID));
                db.update(REMINDERS_TABLE, values, COLUMN_REMINDER_ID + "= ?", new String[] {String.valueOf(old_id)});
                new_id++;

            } while (cursor.moveToNext());
        }

    }
}

I haven't gotten to the point of testing it yet, but even if it works, I'm wondering whether there is a better way of doing this? My reason for asking is because I don't have much experience.

Thank you

EDIT: creating a method that implements Joachim Isaksson's solution:

public void updateRemindersIds(){
    SQLiteDatabase db = this.getWritableDatabase();
    String updateQuery = "UPDATE " + REMINDERS_TABLE + " SET " + COLUMN_REMINDER_ID + " = (" +
                            "SELECT COUNT(*) + 1 FROM " + REMINDERS_TABLE + " r " +
                            "WHERE " + REMINDERS_TABLE + "." + COLUMN_REMINDER_ID + "> r." + COLUMN_REMINDER_ID + ")";

    db.execSQL(updateQuery);
    db.close();

}

I suppose this is correct for Android / Java / SQLite?

Answer 1

As long as they have unique reminder id's, you could renumber the items using a single update;

UPDATE reminders SET reminder_id = (
  SELECT COUNT(*)+1
  FROM reminders r
  WHERE reminders.reminder_id>r.reminder_id
);

An SQLfiddle to test with .