如何在Oracle中解析字符串？

regexp_replace(str, \'.*request=\"([^\"]*)\".*\', \'\\1\')

INSTR(givenstring, stringchartosearch,start_position)

substr(string, starting_position, length)

instr

substr

substr(my_str, 
       -- find request=\" then get index of next char.
       instr(my_str, \'request=\"\') + 9, 
       -- This is the second \" after request. It does not allow for escapes
       instr(substr(my_str,instr(my_str, \'request=\"\')), 2))

SET serveroutput ON

DECLARE
  l_string             VARCHAR2(100) := \'<!-- accountId=\"123\" activity=\"add\" request=\"add user\" -->\';
  l_result_from_substr VARCHAR2(50);
  l_result_from_regexp VARCHAR2(50);
BEGIN

  SELECT SUBSTR(l_string, instr(l_string, \'request=\"\') + 9, instr(SUBSTR(l_string,instr(l_string, \'request=\"\')), \'\"\', 2)-1),
    regexp_replace(l_string, \'.* request=\"([^\"]*)\".*\', \'\\1\')
  INTO l_result_from_substr,
    l_result_from_regexp
  FROM dual;

  dbms_output.put_line(\'Result from substr: \'||l_result_from_substr);
  dbms_output.put_line(\'Result from regexp: \'||l_result_from_regexp);

END;
/