If you needed, here is the oml file.
The test is in the WebScreen1 screen.

While that is certainly a very simple and easy to understand solution, it does mean executing 27 queries to the database (unless you add some paging). Depending on the amount of data, you might take a performance hit. 

Another way could be to use 1 aggregate, and loop over that list. Then insert extra records into the results based on every letter you need. Just an empty record with the letter in the name column. Then, add some css into the table to give those letter rows a different look. (adding extra records, you might need to keep an eye on the index and paging) I think this is similar to what Carlos suggested.

That would probably be my solution as well, but Sylvain must be aware that you cannot insert items into the list you are looping over. Therefore I think the best solution is this:

• Loop over the (sorted) list, determine which indexes new letters start, and add the letter and the index (using CurrentRowNumber) to a temporary list;
• Next, sort the temporary list from highest index to lowest;
• Loop over the temporary list, and use ListInsert to insert the right letter in the right position.

The reason to sort the temp list is that if you loop over it from lowest to highest, you have to take index shift into account (if something needs to be inserted in positions 2 and 5, after inserting at position 2 the next one is now 6). Possible by e.g. adding the CurrentRowNumber of the temp list to the index in the temp list, but reverse sorting is easier I think (though slightly less performant).

Paging is non-trivial in this situation, you're basically stuck with retrieving the entire list at once, unless you want to do some advanced trickery.

You're right Kilian. I just wanted to point out the basic idea. Your solution is what I meant, but you described it way better ;-)