正则表达式
select regexp_instr('but, soft! what light through yonder windows breaks?','l[[:alpha:]]{4}')
as result from dual中{4}是什么意思？
与select regexp_instr('but, soft! what light through yonder windows breaks?','l[[:alpha:]]')
as result from dual返回结果一致。

[解决办法]

SQL code

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