Let's make a custom function MD5:

with DBISAMEngine do
  with Functions.CreateFunction(ftString, 'MD5').Params do
  begin
    CreateFunctionParam(ftString);
  end;
end;

... and write the following code to the DBISAMEngineCustomFunction procedure:

if AnsiCompareText(FunctionName, 'MD5') then
begin
  if FunctionParams[0].IsNull then
    Result := Null;
  else
    Result := AnsiLowerCase(MD5DigestToString(MD5String(FunctionParams[0].AsString)));
end;

... let's 
say I have this query that works properly:

SELECT recno. floor(myfield / 1000) FROM mytable;

... and now modify it like this:

SELECT recno, floor(myfield / 1000) as F, MD5(anotherfield) as M FROM 
mytable;

... and then I try this code:

ShowMessage(tMyTable.FieldByName('F').AsString);

... and it will return 0 and not the correct field value. (I think but I 
am not sure that if I use a grid to display the field values, then it 
works fine but if I don't have a DataSourec and a Grid then it will fail.

---

 Comments and Workarounds

---

The workaround is to declare the function result as an ftMemo data type instead of an ftString data type, but that has the side-effect of making the result set canned.

---

 Resolution

---

Fixed Problem on 10/19/2004 in version 4.13 build 1