title: How to replace occurrence only on the start of the string in Oracle SQL?
body: <p>I have a source column and I want to search for string values starting with 05, 5 971971 and 97105 to be replaced by 9715. As showin in output table. </p>
  
  <p><code>SOURCE         OUTPUT
  0514377920      971514377920
  544233920       971544233920
  971971511233920 971511233920
  9710511233920   971511233920</code></p>
  
  <p>I tried following which works for first case. </p>
  
  <pre><code>SELECT REGEXP_REPLACE ('0544377905', '^(\05*)', '9715')FROM dual;
  </code></pre>
  
  <p>But following is not working, for second case: </p>
  
  <pre><code>SELECT REGEXP_REPLACE ('544377905', '^(\5*)', '9715')FROM dual;
  </code></pre>
  
  <p>Something is wrong with my regular expression. As I am getting: ORA-12727: invalid back reference in regular expression.</p>