Here below is the student data table:

Now we want to create a student ID for every student. The student ID should be: class number + student’s serial number in the class, and the serial number should be two-digit (calculate in cell C1):

=spl("=E(?1).group(Class).(~.(Class+string(#,""00""))).conj().new(~:ID)",A1:B21)

https://c.scudata.com/article/1651916536524
https://c.scudata.com/article/1655083629294
https://c.scudata.com/article/1655170443233