substr/ instr

/*update hr_user_qy0331_ok l
   set l.login_name_new = substr(l.login_name,
                                 1,
                                 instr(l.login_name, '@') - 1) ||
                          to_char(to_date(l.从身份证号码截取出生日期, 'yyyy/mm/dd'), 'mmdd') ||
                          substr(l.login_name, instr(l.login_name, '@')) where l.从身份证号码截取出生日期 is not null
                          and l.同名否 = 'same' and l.login_name is not null*/
                          
                          
 select login_name,instr(a.login_name, '@'),substr(a.login_name, instr(a.login_name, '@')) from hr_user_qy0331_ok a