IDENTITY property does that, but people often want "no gaps", and that is an issue.
What happens if:
Person A creates a new record
Person B does too
SQL allocated ID=1000 to Person A and 1001 to Person B
Then something goes wrong with Person A's insert and that transaction is rolled back. Person B's record 1001 saved OK.
For the next person that needs an ID SQL will assign them 1002, thus ID=1000 is "Missing".
You can assign an ID yourself, e.g. using
but the problem with this is that it becomes a bottleneck for record insertions and, in a busy table, will BLOCK other transactions, hence better to use IDENTITY and live with the "gaps"
What is the difference between your ID (Primary key) column and your [fslno] column?