An error occurs when trying to write the second row to the table. How to fix?

Question

MySQL

MySQL 5.7 has a stored function that writes to the database:

CREATE function `insert_material` (_guid char(36), _name varchar(255)) returns int
BEGIN
declare b_guid binary(16);
set b_guid = unhex(replace(_guid, '-', ''));
insert into Material(guid, name) value(b_guid, _name);
return LAST_INSERT_ID();
END

The problem is that only one record can be made to the table. When trying to make a second entry, an error occurs:

Answer 1

...
insert ignore into Material(guid, name) value(b_guid, _name);
...