There are two fields in the SAP table AUFK, AUFNR and KDAUF, that I cannot differentiate. I searched around in the net, and both are being referred to as "Sales Order Number".
Can somebody kindly explain what the differences are between the two?
AUFNR is not the sales order number. Table AUFK stores the internal orders of the CO module, AUFNR is its number, so the internal order number. Internal order is a CO element (like a cost center), you can post on them. KDAUF is the sales order number (you can post sales orders on internal orders, this is why it is there).