Change Column values in oracle database

SQL> create table mobilephnno (slno varchar2(1), phone varchar2(15)); Table created. SQL> insert into mobilephnno values('1','01744642681'); 1 row created. SQL> insert into mobilephnno values('2','01744642682'); 1 row created. SQL> insert into mobilephnno values('3','01744642683'); 1 row created. SQL> commit; SQL> update mobilephnno set phone=substr(phone,1,2)||replace(substr(phone,3,1),'7','8')|| substr(phone,4,9); 3 rows updated. SQL> select * from mobilephnno; S PHONE - --------------- 1 01844642681 2 01844642682 3 01844642683