Normally, it's very simple to setup serial number for a filed. Just go to the Manage Database then the filed option and check the check box of serial number.
However, in my case, I cannot use this method because I have two different types of invoice numbers. For example, if the invoice is for domestic, I use DH-XXXXX and if it's an international invoice, I use HN-XXXXX
Therefore, I think there is no way for me to use the serial number function for my invoice field. Below is my current method. I have two fields for my invoice number. One is a drop-down menu for my invoice symbol: DH- or HN- and the other is the sequence like 17001, 17002...and so on. But I need to manually enter the sequence myself.
Thus, I am wondering if there is a better way to do it? For example, if I select DH- or HN-, it will generate the sequence number from the last invoice number?
For example, if my last domestic invoice number is DH-17231, it will auto enter DH-17232 when I select my invoice symbol as DH-; and if my last International invoice number is HN-17015, it will auto enter HN-17016 when I selected the invoice symbol as HN- instead????