biraz zorlama bir yapı oldu ama dilerim işinize yarar

select Undertaking_Date, Create_Date,  (strftime('%j',date(strftime('%s',datetime(substr(Undertaking_Date, 7,4) || "-" || substr(Undertaking_Date,4,2)  || "-" || substr(Undertaking_Date, 1,2) || " " || substr(Undertaking_Date, 11))) - strftime('%s',datetime(substr(Create_Date, 7,4) || "-" || substr(Create_Date,4,2)  || "-" || substr(Create_Date, 1,2) || " " || substr(Create_Date, 11))),'unixepoch')) - 1) ||" Gün "|| time(strftime('%s',datetime(substr(Undertaking_Date, 7,4) || "-" || substr(Undertaking_Date,4,2)  || "-" || substr(Undertaking_Date, 1,2) || " " || substr(Undertaking_Date, 11))) - strftime('%s',datetime(substr(Create_Date, 7,4) || "-" || substr(Create_Date,4,2)  || "-" || substr(Create_Date, 1,2) || " " || substr(Create_Date, 11))),'unixepoch') as "Fark"  from Deneme