The problem we need to solve:

• In this particular field on the interface file, we want to show the work order, if the work order has been defined.
• BUT, if it has not been defined, we want to use the distribution code.
• UNLESS the transaction is for a BURDEN posting, then we need to replace the last four characters of the work order with a constant 8299.

A pseudo-code interpretation could look like this:

decode 
   (WORK_ORDER,              <--- Check the Work Order
      null , DISTR_CODE        <--- If it is NULL (not provided) then use the Distribution Code
      ,                        <--- otherwise (not a paired set of values for the DECODE ...
      decode (GL_ACCOUNT_CODE, <--- Check the GL ACCOUNT CODE
         'D-BURDEN EXP',       <--- If it is the code used for Burden then ...
         substr(WORK_ORDER,1,    <--- Get the Work Order from the first character 
         to where the ‘/’ is in WORK_ORDER)
         ||'/8299',              <--- Concatenate the constant value
        WORK_ORDER)            <--- Otherwise just use the WORK ORDER
       )

We see that these pieces are available in the GL BUFFER:

• WORK_ORDER 523 for 50 chars.
• DISTR_CODE 51 for 50 chars.
• GL_ACCOUNT_CODE 101 for 16 chars.

We will want to remove trailing blanks and so we can replace them as follows

Now we can replace the pseudo code with the real derivations:

decode 
  (rtrim(substr(~,523,50)), 
     null,rtrim(substr(~,51,50))
     ,
     decode (substr(~,101,12),
       'D-BURDEN EXP',
       substr(rtrim(substr(~,523,50)),1,
       instr(substr(~,523,50),'/')-1)
       || '/8299',
      rtrim(substr(~,523,50)))
      )