I want to trim a string to a specified length. If the string is shorter, I don't want to do anything. I found a function substr() which does the job. However there is nothing in the Oracle documentation what happens if the string is shorter, than maximal length.
For example this:
select substr('abc',1,5) from dual;
returns 'abc', which is what I need.
I'd like to ask if this is safe, because the function seems not to be defined for this usage. Is there a better way how to truncate?
This is an interesting question. Surprisingly, the documentation doesn't seem to cover this point explicitly.
I think what you are doing is quite safe. substr() is not going to "add" characters to the end of the string when the string is too short. I have depended on this behavior in many databases, including Oracle, over time. This is how similar functions work in other databases and most languages.
The one sort-of-exception would be when the original data type is a char() rather than varchar2() type. In this case, the function would return a string of the same type, so it might be padded with spaces. That, though, is a property of the type not really of the function.