Help with sign and replacestr functions in SQL

Question

I am trying this:
In a full name if the Middle Initial is null then add an additional space between the First name and last name else select the full name itself.
For to check for the spaces I am subtracting first occurrence of space - second occurrence of space using instr function
I have to use sign function to check for "-value", if the value is -ve then don't do any thing and if it is equal to 0 add one more space to the name.
But how can i use decode here to select the original column if sign is a negative value.
My sql:
IIF(SIGN(INSTR(o_full_name,' ')- (INSTR(o_full_name,' ',1,2)))=0,REPLACESTR(1,o_full_name,' ',' '))
gow can i use decode in place off IIF

Answer 1

this examples might help if the names are in separate columns.
SQL> create table telephone_list
  2  (first_name     varchar2(20),
  3   middle_initial varchar2(2),
  4   last_name      varchar2(20));
Table created.
SQL> insert into telephone_list
  2  values
  3  ('Scott',null,'Tiger');
1 row created.
SQL> insert into telephone_list
  2  values
  3  ('John','T','Perl');
1 row created.
SQL> insert into telephone_list
  2  values
  3  ('Kim',null,'Molit');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from telephone_list;
FIRST_NAME           MI LAST_NAME
Scott                   Tiger
John                 T  Perl
Kim                     Molit
SQL> select decode(middle_initial,null,first_name||' '||last_name,
  2                                    first_name||' '||middle_initial||' '||last_name)
  3         full_name
  4    from telephone_list;
FULL_NAME
Scott Tiger
John T Perl
Kim Molit
SQL> is the name in one column only? please post a sample data. thanks.