oracle 正則表達式

select * from (
select t.platform as platform,
t.version_id as version_id,
t.version as oversion,
regexp_substr(t.version, '^[[:digit:]\.]') as bigver,
decode(regexp_substr(version, '^[[:digit:]\.]'),4,regexp_substr(version, '^[:digit:][:digit:][:digit:][:digit:]+)+$') is not null
and t.version != 'all'
)
where version is not null