When running with sql_mode=ORACLE, MariaDB should treat the second argument (the position) to "substr" in Oracle way: If position is 0, then it is treated as 1.

Currently MariaDB returns an empty string in case when the position is 0:

select substr('abc',0,3);

+-------------------+

| substr('abc',0,3) |

+-------------------+

|                   |

+-------------------+

This screenshot from an Oracle session demonstrates that 0 is translated to 1:

SQL> select substr('abc',0,3) from dual;

SUB

---

abc