VAR ClientArticles = CALCULATETABLE(VALUES('BDD'[Type d'Articles]), ALLEXCEPT('BDD', 'BDD'[Code client]))
RETURN
SWITCH(
TRUE(),
COUNTROWS(ClientArticles) > 1, "Mixte",
COUNTROWS(ClientArticles) = 1 && MAX('BDD'[Type d'Articles]) = "A", "A",
COUNTROWS(ClientArticles) = 1 && MAX('BDD'[Type d'Articles]) = "B", "B",
"Autre"
)