Oracle slow CLOB / STRINGS

For those of you that have used oracle string functions such as SUBSTR you'll know that it can end up being very slow if you are trying to repetedly scan through long strings of data.

I sometimes use this kind of function when looping through rows of a CSV or XML file, it gets increasingly slow as it gets further in to the string.

To get around this once you have processed a row of a CSV file chop the bit you have finished with off and then there is not as much to search through next time around.