SQL Server 2019

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create table mytable(name nvarchar(max))
insert into mytable
values 
	('ABC_DEFG_HIJKL'), 
	('A_B_C'),
	('A_B_C_D')


3 rows affected

select name,
	json_value(obj, '$[0]') name1,
	json_value(obj, '$[1]') name2,
	json_value(obj, '$[2]') name2,
	json_value(obj, '$[3]') name4
from mytable t
cross apply (values('["' + replace(name, '_', '", "') + '"]')) x(obj)


name
name1
name2
name2
name4


ABC_DEFG_HIJKL
ABC
DEFG
HIJKL
null

A_B_C
A
B
C
null

A_B_C_D
A
B
C
D