Creat same serial number but I set the serial number unique
The database is used for warehouse in/out administration; and there is an in/out record list on which each record should have a unique serial number that is generated automatically. But sometimes it generates the same serial number, for example serial number A00001 appeared twice in the list; and several days later the repeating serial number (the second A00001 in this case) disappeared with the record. That changes the content of the list.
I don't konw what happend.