在＆＃34;之前和之后获取子串。＆＃34;完全停止，如果未找到则获取NULL

Question

我希望在＆＃34;之后和之前得到子字符串。＆＃34;，例如

Furniture.Chair 我需要＆＃34; Category1＆＃34;栏目和主席在＆＃34;类别2＆＃34;列，但如果字符串是这样的：

家具。然后我需要＆＃34; Null＆＃34; in＆＃34; Category2＆＃34;柱。但我无法做到这一点。 请参阅以下屏幕进行校正：

由于

Answer 1

with data (val) as
(
  select 'furniture' from dual union all -- without the dot 
  select 'furniture.' from dual union all -- dot at the end
  select '.furniture' from dual union all -- dot at the beginning
  select null from dual union all -- no input
  select 'home owners.home.home' from dual union all -- if more than one dot is found
  select 'health and beauty.skin care' from dual -- words followed by dot followed by words
)
, coll as
(
select 
  val, 
  -- [^\.]+  any character sequence other than dot (+ is for one or more)
  -- (\.|) find a dot or nothing - eg. 'furniture' with a dot 
  -- (([^\.]+)) the outer brackets capture the first group \1; 
  --            the first inner brackets capture the second group
  --            the last argument to the regexp_substr below ie. '2' tells 
  --            method our interest is in the second group within the match 
  --            identified by (([^\.]+)(\.|)) 
  regexp_substr(val, '(([^\.]+)(\.|))', 1, 1, null, '2') as first,  
  regexp_substr(val, '(\.(.*))', 1, 1, null, '2') as the_rest 
from data
)
select 
  val, 
  case when first is null then 'Unknown Category' else first end as first,
  case when first is null then 'Unknown Category' else first end as the_rest
from coll
;