I have a SQL where I am using a UNION. I would like to know if there would be a way to obtain the same without using the UNION.

The SQL is like this:

SELECT MainTable.Numero FROM MainTable INNER JOIN ChildTable;
 ON MainTable.IGroupe=ChildTable.IGroupe WHERE ChildTable.No_Membre=7;
 UNION;
SELECT MainTable.Numero FROM MainTable WHERE MainTable.IGroupe=0