Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
CREATE TABLE table_name(email) AS
SELECT 'raju.das@example.com' FROM DUAL UNION ALL
SELECT 'javed.khan@example.com' FROM DUAL UNION ALL
SELECT 'Amit.kumar.bera@example.com' FROM DUAL;
3 rows affected

SELECT SUBSTR(local_part, INSTR(local_part, '.', -1) + 1) AS last_name,
       SUBSTR(domain, 1, INSTR(domain, '.') - 1) AS domain
FROM   (
  SELECT SUBSTR(email, 1, INSTR(email, '@', -1) - 1) AS local_part,
         SUBSTR(email, INSTR(email, '@', -1) + 1) AS domain
  FROM   table_name
)


LAST_NAME
DOMAIN


das
example

khan
example

bera
example


SELECT REGEXP_SUBSTR(email, '([^.]+)@([^.]+)', 1, 1, NULL, 1) AS last_name,
       REGEXP_SUBSTR(email, '([^.]+)@([^.]+)', 1, 1, NULL, 2) AS domain
FROM   table_name;


LAST_NAME
DOMAIN


das
example

khan
example

bera
example