Chanllenging task in hierarchial queries

Question

I have a table sk_main
create table sk_main(empno number, mgr number)
insert into sk_main values (1,null);
insert into sk_main values (2,1);
insert into sk_main values (3,1);
insert into sk_main values (4,2);
insert into sk_main values (6,2);
insert into sk_main values (5,3);
Another Table
create table sk_recalc(id number, tag_val varchar2(1000))
Initially table is loaded like this,
insert into sk_recalc
select rownum,ltrim(sys_connect_by_path(empno,'\'),'\') from sk_main
start with mgr is null
connect by prior empno=mgr;
Output1:
ID|TAG_VAL
1|1
2|1\2
3|1\2\4
4|1\2\6
5|1\3
6|1\3\5
Now assume below DML's Happened to sk_main table,
insert into sk_main values(7,2);
update sk_main set mgr=7 where empno=4
so now tag_val's become
Output2:
ROWNUM|LTRIM(SYS_CONNECT_BY_PATH(EMPNO,'\'),'\')
1|1
2|1\2
3|1\2\6
4|1\2\7
5|1\2\7\4
6|1\3
7|1\3\5
now if we see output1 and output2,
sk_recalc() output is below before dml operations to sk_main table, after dml operations, sk_recalc() table should get update for those records which are different
Output1:
ID|TAG_VAL
1|1
2|1\2
3|1\2\4
4|1\2\6
5|1\3
6|1\3\5
and after dml operations sk_recalc() table should get update for those records which are different after dml operations, for example
1,1\2,1\2\6,1\3,1\3\5 are same before and after dml operations so this id's should not change in sk_recalc table,
1\2\4 will become 1\2\7 and 1\2\7\4 comparing this 1\2\4 is substring of 1\2\7\4 so 1\2\7\4 will be updated with id of 1\2\4 in the table and 1\2\7 will be inserted as new one,
and finally output should look like:
Required Output
ID|TAG_VAL
1|1
2|1\2
*3|1\2\7\4*
4|1\2\6
5|1\3
6|1\3\5
*7|1\2\4*
Thanks for your help in advance,

Answer 1

MERGE INTO sk_recalc s
USING
(select rownum id,ltrim(sys_connect_by_path(empno,'\'),'\') tag_val from sk_main
start with mgr is null
connect by prior empno=mgr) t
ON (s.id = t.id)
WHEN MATCHED THEN
  update set tag_val = t.tag_val
WHEN NOT MATCHED THEN
  insert values ( t.id,t.tag_val);