It's a nice little setup for augmenting Gail's fine explanation with some tables. Is id_object the PK of the object table, by any chance?
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden