sql - 如何在 PL/SQL 中查找字符串中不同字符的计数和名称

Question

我对 PL/SQL 很陌生，我需要获取字符串中不同字符的名称和计数。例如，如果我有一个字符串str="helloexample"，我需要得到不同字符的输出str，即heloxamp。

我怎样才能做到这一点？

Answer 1

您可以按如下方式使用正则表达式：

SET serveroutput ON
DECLARE
     str        VARCHAR2(20):='helloexample';
     str_length NUMBER;
     c          VARCHAR2(20):=NULL;
     d          NUMBER;
BEGIN
     str_length:=LENGTH(str);
     FOR i IN 1..str_length
     LOOP
          IF regexp_instr(c,SUBSTR(str,i,1))>0 THEN
               NULL;
          ELSE
               c:=c||SUBSTR(str,i,1);
          END IF;
     END LOOP;
     dbms_output.put_line(c);
END;

答案是：

heloxamp

Answer 2

如果 WM_CONCAT 不适合你，你可以使用这个技巧：

select rtrim(xmlagg(xmlelement(e, str)).extract('//text()'), ',') as output
  from (select substr(str, level, 1) str, level l,
               row_number() over (partition by substr(str, level, 1) 
                                      order by level) rn
          from (select 'helloexample' str  from dual) d
        connect by level <= length(str)
        order by level)
 where rn = 1;


SQL> select rtrim(xmlagg(xmlelement(e, str)).extract('//text()'), ',') as output
  2    from (select substr(str, rownum, 1) str, level l,
  3                 row_number() over (partition by substr(str, rownum, 1) order by level) rn
  4            from (select 'helloexample' str  from dual) d
  5          connect by level <= length(str)
  6          order by level)
  7   where rn = 1;

OUTPUT
--------------------------------------------------------------------------------
heloxamp