select regexp_instr('but, soft! what light through yonder windows breaks?',
                    'l[[:alpha:]]{4}') as result  --匹配l[[:alpha:]]{4}表示l后面有4个字母
  from dual
       
select regexp_instr('but, soft! what light through yonder windows breaks?',
                    'l[[:alpha:]]') as result   --匹配l[[:alpha:]]后面一个字母
  from dual