DBMS_RANDOM

DBMS.RANDOM: allows to generate the random number of values.

dbms_random.value(lowerlimit,highlimit): Is used to generate the random numeric values in a given limit.
eg:dbms_random.value(1,1000)

dbms_random.string(opt,length): is used to generate the random string, in a specified length.
eg:dbms_random.string('U',10)
'u' or 'U':
Upper case alpha characters
'l' or 'L':
Lower case alpha characters
'a' or 'A':
Upper and lower case alpha characters
'x' or 'X':
Upper alpha and numeric characters
'p' or 'P':
Any printable character