Calcola i giorni lavorativi in ​​Oracle SQL (nessuna funzione o procedura)

La soluzione, finalmente:

SELECT OrderNumber, InstallDate, CompleteDate,
  (TRUNC(CompleteDate) - TRUNC(InstallDate) ) +1 - 
  ((((TRUNC(CompleteDate,'D'))-(TRUNC(InstallDate,'D')))/7)*2) -
  (CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SUN' THEN 1 ELSE 0 END) -
  (CASE WHEN TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SAT' THEN 1 ELSE 0 END) as BusinessDays
FROM Orders
ORDER BY OrderNumber;

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