create table TEST_NUMBER
(id number(4,1));


insert into TEST_NUMBER
values(1234.789888888888);

select *
from TEST_NUMBER;

123.8

select cast(id as number(1,1))
from TEST_NUMBER;

ORA-01438: value larger than specified precision allowed for this column
01438. 00000 -  "value larger than specified precision allowed for this column"
*Cause:    When inserting or updating records, a numeric value was entered
           that exceeded the precision defined for the column.
*Action:   Enter a value that complies with the numeric column's precision,
           or use the MODIFY option with the ALTER TABLE command to expand
           the precision.

i want result like 1.8

SELECT CAST (123.78888 AS NUMBER (4, 1)) 
  FROM DUAL;

----------------------------
                       123,8
1 row selected.