USE test;

DROP TABLE IF EXISTS errtab;

CREATE TABLE errtab (                 
   id int(11) NOT NULL,                
   parent_id int(11) DEFAULT NULL,     
   name varchar(10) DEFAULT NULL,      
   PRIMARY KEY (id),                   
   KEY ind_parent_id (parent_id)     
) ENGINE=InnoDB;

insert into errtab (id, parent_id, name) values
(10,NULL,'A'),
(20,10,'B'),
(30,10,'C'),
(40,NULL,'D'),
(50,40,'E'),
(60,40,'F'),
(70,NULL,'J');

SELECT id FROM errtab WHERE parent_id IS NOT NULL ORDER BY id DESC LIMIT 1;
SELECT * FROM errtab WHERE parent_id IS NOT NULL ORDER BY id DESC LIMIT 1;