Increment value when the field is the same - sql

Question

First, I'm sorry for the ambiguous title.
Here's my problem :
I'm using Access and I have this table :
+--------+-----------+
| PARENT | CHILD |
+--------+-----------+
| JOHN | TANIA |
| JOHN | ROBERT |
| JOHN | APRIL |
| HELEN | TOM |
| HELEN | GABRIELLE |
+--------+-----------+
And I would like to add a column like this with queries or VBA code :
+--------+-----------+---------+
| PARENT | CHILD | LIST |
+--------+-----------+---------+
| JOHN | TANIA | CHILD 1 |
| JOHN | ROBERT | CHILD 2 |
| JOHN | APRIL | CHILD 3 |
| HELEN | TOM | CHILD 1 |
| HELEN | GABRIELLE | CHILD 2 |
+--------+-----------+---------+
I want to do this because at the end, I want to run a cross tab query. I'm only missing that last column to create that query.
I tried to do it in a recordset, but my database starts bloating after a couple of rst.Update (I have 700k+ rows)
I created a temporary table and used UPDATE queries but it just takes too much time.
I think there might be a SQL code that would do what I need, but I just can't figure it out. I hope you could help me, thanks :)

Answer 1

You can do something like the below, but it would be much better with some sort of IDs:
SELECT Parent.PARENT,
Parent.CHILD,
(SELECT Count(*)
FROM Parent p
WHERE p.Parent=Parent.Parent
AND p.Child<=Parent.Child) AS ChildNo
FROM Parent
ORDER BY Parent.PARENT, Parent.CHILD;
Parent is the name of the table.