title: Oracle: SELECT to_number('3+11+7') FROM dual; gives ora-01722
body: <p>I am using oracle 11g R2. When i query SELECT to_number('3+11+7') FROM dual. It gives ora-01722.
  and when i remove single quotes, SELECT to_number(3+11+7) FROM dual. Then it gives answer 21.
  I just removed single quotes from string. How can i do it with built in functions.
  Thanks.</p>