In Oracle, I want to know if a string value is numeric only. How can I do this?

To test a string for numeric characters, you could use a combination of the LENGTH, TRIM, AND TRANSLATE functions built into Oracle.
You can use the following command:

LENGTH(TRIM(TRANSLATE(string1, ' +-.0123456789', ' ')))

string1 is the string value that you are testing
This function will return a null value if string1 is numeric. It will return a value "greater than 0" if string1 contains any non-numeric characters.

For example,

LENGTH(TRIM(TRANSLATE('123b', ' +-.0123456789',' ')));	would return 1
LENGTH(TRIM(TRANSLATE('a123b', ' +-.0123456789',' ')));	would return 2
LENGTH(TRIM(TRANSLATE('1256.54', ' +-.0123456789',' ')));	would return null
LENGTH(TRIM(TRANSLATE ('-56', ' +-.0123456789',' ')));