oracle去掉字符串中重复的子串

目前有如下2种方式

1.有特定关联规则的,以字符串维度去重
create or replace function fun_rep_repeat_str(p_str varchar2)
 return varchar2 deterministic  is

type  v_type is table of varchar2(4000);
v_tab v_type;
v_res varchar2(4000);
cursor c_get_str is
select regexp_substr(p_str, '[^;]+', 1, level) str
  from dual
connect by level <= length(regexp_replace(p_str, '[^;]')) + 1;

begin
 open c_get_str;
 fetch c_get_str bulk collect into v_tab;
 close c_get_str;  
 --集合去重
 v_tab:=set(v_tab);

 for x in 1.. v_tab.count loop
   v_res:=v_res||v_tab(x)||';';
 end loop;
  return rtrim(v_res,';');
end;

select fun_rep_repeat_str('数学;乒乓球;篮球;数学;数学;体育;乒乓球') from dual;


2.如果是去掉重复单个子符,上面的也可以用
select regexp_replace('a;b;v;a',';a','',2) from dual;
或者:
create or replace function fun_repeat_char(p_str varchar2)
 return varchar2 deterministic  is

v_res varchar2(4000);
v_count pls_integer;
v_temp varchar2(4000);

begin
  if p_str is null or length(p_str) = 1 then
    return p_str;
  end if;
  v_count := length(p_str) - 1;
  for x in 1 .. v_count loop
    v_temp := substr(p_str, x, 1);
    if nvl(instr(v_res, v_temp, 1, 1),0)<= 0 then
      v_res := v_res || v_temp;
    end if;
  end loop;
  return v_res;
end;
/
select fun_repeat_char('AAAAABBDHDKAJHDKASLKASJKLASLAAA') from dual;