Oracle 18c

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create table t42 (number_str varchar2(16))
/
insert into t42 
select '4229,4' from dual union all
select '3234,3' from dual union all
select '125,5' from dual  union all
select '23,424242' from dual 
/
4 rows affected

select number_str
       ,cast(replace(number_str, ',', '.') as number(38,7)) as number_nbr
from t42
/


NUMBER_STR
NUMBER_NBR


4229,4
4229.4

3234,3
3234.3

125,5
125.5

23,424242
23.424242