Optimize query for yii2 - mysql

Question

this query is getting the right data i want, but this is so slow and heavy on our server, with only 5417 rows of data. how would i optimize this query in query builder or yii2 framework way?
SELECT t1.id
FROM tbl_ticket t1
WHERE NOT EXISTS
( SELECT 1
FROM tbl_ticket
WHERE parent_id = t1.id
)
AND parent_id =0
UNION ALL
SELECT MAX( id )
FROM tbl_ticket
WHERE parent_id <>0
GROUP BY parent_id
ORDER BY id ASC

Answer 1

( SELECT t1.id
FROM tbl_ticket t1
LEFT JOIN tbl_ticket t2 ON t2.parent_id = t1.id
WHERE t2.id IS NULL
AND t1.parent_id = 0 )
UNION ALL
( SELECT MAX( id )
FROM tbl_ticket
WHERE parent_id <> 0
GROUP BY parent_id )
ORDER BY id ASC
The first SELECT seems to be finding ids that have no children and no parents. Correct?
The second SELECT seems to be finding the last sibling in each family, excluding Adam and Eve. Is that what you intended?
I added parentheses to move the ORDER BY away from the second SELECT to the entire query. Is that what you intended?
To make that query run 'fast', you need
INDEX(parent_id, id)
I assume, you already have PRIMARY KEY(id). (Please provide SHOW CREATE TABLE tbl_ticket.)

Answer 2

here is the table:
CREATE TABLE IF NOT EXISTS tbl_ticket (
id int(9) NOT NULL AUTO_INCREMENT,
parent_id int(11) NOT NULL,
ticket_title varchar(250) NOT NULL,
location_id varchar(250) CHARACTER SET latin1 NOT NULL,
status int(11) NOT NULL,
remarks varchar(250) CHARACTER SET latin1 NOT NULL,
r_date datetime NOT NULL,
d_date datetime NOT NULL,
hd_user_username varchar(250) CHARACTER SET latin1 NOT NULL,
hd_user_email varchar(250) CHARACTER SET latin1 NOT NULL,
description varchar(3000) NOT NULL,
attachment varchar(250) NOT NULL,
created_by varchar(250) NOT NULL,
updated_by varchar(250) NOT NULL,
room_no varchar(250) NOT NULL,
gsm varchar(250) NOT NULL,
file_mime_type varchar(250) NOT NULL,
file_original_name varchar(250) DEFAULT NULL,
file_size varchar(250) DEFAULT NULL,
file_extension varchar(250) DEFAULT NULL,
acknowledged varchar(250) DEFAULT NULL,
ip_address varchar(20) DEFAULT NULL,
hostname varchar(255) DEFAULT NULL,
useragent text,
closing_remark varchar(2048) DEFAULT NULL,
rating int(6) DEFAULT NULL,
is_student int(2) DEFAULT NULL,
installation int(1) DEFAULT NULL,
type int(1) DEFAULT NULL,
PRIMARY KEY (id),
KEY id (id),
KEY parent_id (parent_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=5428 ;