Oracle 18c

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select regexp_substr('D*(A+B)-(C+A)*(C+A)', '[^+*/()-]+', 1, level) from dual
  connect by regexp_substr('D*(A+B)-(C+A)*(C+A)', '[^+*/()-]+', 1, level) is not null 

REGEXP_SUBSTR('D*(A+B)-(C+A)*(C+A)','[^+*/()-]+',1,LEVEL)

D

A

B

C

A

C

A

select regexp_replace('D*(A+B)-(C+A)*(C+A)', '([+*/()-])', '|\1|') from dual

REGEXP_REPLACE('D*(A+B)-(C+A)*(C+A)','([+*/()-])','|\1|')

D|*||(|A|+|B|)||-||(|C|+|A|)||*||(|C|+|A|)|

select regexp_substr(
  regexp_replace('D*(A+B)-(C+A)*(C+A)', '([+*/()-])', '|\1|'),
  '[^|]+', 1, level)
from dual
connect by regexp_substr(
  regexp_replace('D*(A+B)-(C+A)*(C+A)', '([+*/()-])', '|\1|'),
  '[^|]+', 1, level) is not null

REGEXP_SUBSTR(REGEXP_REPLACE('D*(A+B)-(C+A)*(C+A)','([+*/()-])','|\1|'),'[^|]+',1,LEVEL)

D

*

(

A

+

B

)

-

(

C

+

A

)

*

(

C

+

A

)