How do i auto-decrement primary key value in SQlite Android

Question

I have a tables in android SQLite and I am trying to figure out how to reset the KEY_ID, I read that: DELETE FROM tablename should delete everything and reset the autoincremement field back to 0 but when I do this it just deletes the data. When a new record is inserted the autoincrement picks up where it left off before the delete. I have implemented a longitemclicklistner on list, it gets the position and i want to delete the particular item from the list. Here is my code

public void deleteContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();
        getWritableDatabase().delete(TABLE_CONTACTS, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) } );


        db.close();
    }

Here is the code in onlongclicklistner

 public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                     int pos, long id) {
                // TODO Auto-generated method stub

                Log.v("long clicked","pos"+" "+pos);

                final int p=pos+1;

                final AlertDialog.Builder b = new AlertDialog.Builder(MainActivity.this);
                b.setIcon(android.R.drawable.ic_dialog_alert);
                b.setMessage("Are you sure you want to DELETE this Entry?");
                b.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                           // continue with delete

                            db.getWritableDatabase();
                            db.deleteContact(db.getContact(p));
                            Intent i = new Intent(MainActivity.this,MainActivity.class);
                            startActivity(i);
                        }
                });
                b.setNegativeButton("No", new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                            // do nothing
                        }
                });

                b.show();

         }

The problem is, id1 is created then id2 is created but when i delete id2 and create a new contact, it gets the id3. i want it to get id2

Answer 1

Why would you need that? It'll make inserts extremely slow. Suppose you have data 1,2,3,4....700, and you deleted 2 what would you do? move all the numbers up? (re-insert)?

or you'll set the next insert index to 2? right then... now delete 18, 45, 70. And insert a new row. After inserting to 18... it has to search for 45? lets say you keep a track of all the empty spaces as well for now, even then how would you cater for removing in random order 205, 102, 300, 50

You can use heap for storing available indexes, but it makes no sense as well. Maybe if you have some specific use case and share that with us we'll be able to help you better.

Answer 2

That's a feature of AUTOINCREMENT. To make the keys reused, change the column definition from

INTEGER PRIMARY KEY AUTOINCREMENT

to just

INTEGER PRIMARY KEY

Further reading: http://sqlite.org/autoinc.html