Oracle 18c

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ALTER SESSION SET NLS_DATE_FORMAT = 'yyyy-mm-dd HH24:MI:SS';
CREATE FUNCTION db_banner
RETURN VARCHAR2 DETERMINISTIC
IS
  v_version VARCHAR2(100);
BEGIN
  SELECT $IF DBMS_DB_VERSION.VERSION < 18
         $THEN banner
         $ELSE banner_full
         $END
  INTO   v_version
  FROM   v$version
  WHERE  ROWNUM = 1;

  RETURN v_version;
END;
/
SELECT db_banner()
FROM   dual


DB_BANNER()


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0