Can anyone tell me how to get the records where UNIT has the numeric values?

UNIT_KEY(INT) UNIT(VARCHAR)
1000 ABCDE
2000 20
3000 10
4000 30
5000 HAHA

The result should be
UNIT_KEY(INT) UNIT(VARCHAR)
2000 20
3000 10
4000 30

Think this should work :-
SELECT UNIT_KEY, UNIT from table where upper(UNIT) = UNIT and lower(UNIT) = UNIT

the example above will not work on " ' , - and so on.
You can try using translate function:

SELECT UNIT_KEY, UNIT from table
where length(translate('UNIT', '', '1234567890'))=0