group by like string I have a table employee in this table i have id company_name employee_id

1 abc  2015_acb_1 
2 abc  2015_acb_2 
3 abc  2015_acb_3 
4 abc  2015_acb_4
5 xyz  2016_xyz_9 
5 xyz  2017_xyz_2 
5 xyz  2016_xyz_3 
5 xyz  2019_xyz_5


I want to select unique string such as from employee table 

_abc_
_xyz_


i have try select employee_id where employee_id like %_%; its not giving as i expected
SELECT DISTINCT SUBSTRING(employee_id FROM 5 FOR 5)
FROM employee;



  some of record contains 3 to 4 _ symbol and position is different


SELECT DISTINCT CONCAT('_',
                       SUBSTRING_INDEX(SUBSTRING_INDEX(employee_id, '_', 2), '_', -1),
                       '_')
FROM employee;