MySQL 5.6

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create table treestructure(name varchar(50),   path varchar(100), pos_left int,pos_right int,pos_level int)

insert into treestructure(name, pos_left,pos_right ,pos_level ) values('folder1',   207,          214,           1);
insert into treestructure(name, pos_left,pos_right ,pos_level ) values('file1',     208,          209,           2);
insert into treestructure(name, pos_left,pos_right ,pos_level ) values('file2',     210,          211,           2);
insert into treestructure(name, pos_left,pos_right ,pos_level ) values('file3',     212,          213,           2);
update treestructure t
left join treestructure ts on ts.pos_level=t.pos_level-1 and t.pos_left between ts.pos_left and ts.pos_right  and  t.pos_right between ts.pos_left and ts.pos_right
set t.path=(case when t.pos_level=1 then t.name else concat(ts.name,'/',t.name) end);
 
select*from treestructure


name
path
pos_left
pos_right
pos_level


folder1
folder1
207
214
1

file1
folder1/file1
208
209
2

file2
folder1/file2
210
211
2

file3
folder1/file3
212
213
2

name	path	pos_left	pos_right	pos_level
folder1	folder1	207	214	1
file1	folder1/file1	208	209	2
file2	folder1/file2	210	211	2
file3	folder1/file3	212	213	2