ORACLE: OCA-047-question and experiment (7)-regexp_replace usage

Question:

Answer: give two examples to understand

Example 1:

SQL> select phone_number,  2  REGEXP_REPLACE(t.phone_number,'([[:digit:]]{3})\.([[:digit:]]{3})\.([[:digit:]]{4})',  3  '(\1)\2-\3') "PHONE_NUMBER"  4  from employees t; PHONE_NUMBER         PHONE_NUMBER-------------------- --------------------------------------------------------------------------------515.123.4567         (515)123-4567515.123.4568         (515)123-4568515.123.4569         (515)123-4569590.423.4567         (590)423-4567590.423.4568         (590)423-4568590.423.4569         (590)423-4569

Example 2:

SQL> select phone_number,  2  REGEXP_REPLACE(t.phone_number,'([[:digit:]]{3})\.([[:digit:]]{3})\.([[:digit:]]{4})',  3  '(\2)\1-\3') "PHONE_NUMBER"  4  from employees t; PHONE_NUMBER         PHONE_NUMBER-------------------- --------------------------------------------------------------------------------515.123.4567         (123)515-4567515.123.4568         (123)515-4568515.123.4569         (123)515-4569590.423.4567         (423)590-4567590.423.4568         (423)590-4568