Fehlende Benutzer-Avatare, Massenlöschung?

[IAmGav (Gavin Perch)]

Vielleicht ist das das, wonach du suchst

Reset all avatars back to default

We would like to reset all users back to default avatar (the first letter of their username). I saw this post where @codinghorror mentions to run a query. But can someone please provide the query to reset this? Thanks in advance