Using SQL we can create a user-defined function (UDF) for calculating the number of business/working dates between two dates, similar to the NETWORKDAYS function for Microsoft Excel.

Creating the SQL function:
We can execute the following SQL code to create our SQL function. You can either run the below scripts from the Run SQL script option from IBM i Access client solutions (ACS) or on IBM i green screen, write the script within a source member of source type SQL at the location libname/srcpfname and then use RUNSQLSTM SRCFILE(libname/srcpfname) SRCMBR(srcmbrname) COMMT(*NONE) DFTRDBCOL(libname) DBGVIEW(*SOURCE) command to execute this script to create SQL function.

create or replace function libname.workingday(startdate DATE,
enddate DATE)
returns INTEGER
language SQL
is deterministic
begin
  declare workingday INTEGER default 0;
  declare tempdate DATE;
  set tempdate = startdate;
  while days(tempdate) <= days(enddate) do
    if dayofweek_iso(tempdate) <> 6 and
       dayofweek_iso(tempdate) <> 7 then
      set workingday = workday + 1;
     end if;
     set tempdate = date(days(tempdate) + 1);   
  end while;
  return workingday; 
end; 

Explanation of the code:
Line 1 -2: Create and replace function workingday that accepts two parameters startdate and enddate of type date.
Line 3: The SQL function returns an integer value which is the number of business/working days.
Line 4-5: Language is SQL and it is deterministic i.e. it returns the same value on the same input dates each time.
Line 6: begin of the function
Line 7: Declare workingday variable of type integer and initialize with value 0.
Line 8: Declare tempdate variable of type date.
Line 9: set the value of tempdate as startdate.
Line 10-16: Run the while loop until days of tempdate <= days of enddate. Days() function returns the integer representation of the date i.e. for Jan 1, 0001(0001-01-01) it returns 1, for (0001-01-02) it returns 2 and so on. Then we check if tempdate is not the 6th and 7th day of the week using DAYOFWEEK_ISO() function then we set the workingday as workingday + 1 i.e. increment by 1 and no increment when tempdate is the 6th and 7th day of the week. After end if; we increment the tempdate by 1 i.e. increment the number of days extracted from tempdate and convert back to date date(days(tempdate) + 1)and while loop end.
Line 17: Return the workingday value.
Line 18: end of function.
Important Point:
Once the function was created an object of the type *SRVPGM and attribute CLE was created in the specified library.

How to call SQL function from Run SQL script ACS or STRSQL session on IBM i:

select libname.workingday('2024-09-05','2024-09-10) from sysibm.sysdummy1

the number of business/working days returned is 4. Since the 5th is Thursday and the 10th is Tuesday and there are total days in between these two dates are 6 and non-working days are 2 i.e. 7th and 8th (Saturday and Sunday) therefore working days are only 4.