How to get hierarchical data from two tables in oracle?

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Question :

I have two tables table1 and table2, I need hierarchical output by joining of both of the tables.

Table1 contains three categories CAT1, CAT2 and CAT3 with one Foreign key i.e. F_ID which is a primary key of another table table2 which contains one more column i.e.VAL.

TABLE 1
-----------------
CAT1        CAT2        CAT3        F_ID
A           a           aa          1
A           a           ab          2
A           b           ba          3
A           b           bb          4
B           c           ca          5
B           c           cb          6
B           d           da          7


TABLE 2
-------------------
F_ID    VAL
1       4
2       6
3       4
4       1
5       6
6       6
7       9

Now i need the data in the below format, where every category and sub-category contains the total sum of VAL.

Need Data in below Format from the above table
----------------------------------------------
A       -       -       15
A       a       -       10
A       a       aa      4
A       a       ab      6
A       b       -       5
A       b       ba      4
A       b       bb      1
B       -       -       21
B       c       -       12  
B       c       ca      6
B       c       cb      6
B       d       -       9
B       da      da      9

Please help me.

Answer :

Use grouping sets. You can try it here.

select cat1, cat2, cat3, sum(val) as val
  from t1 join t2 on t1.f_id = t2.f_id
group by grouping sets ((cat1),(cat1, cat2),(cat1, cat2, cat3))
order by cat1, cat2 nulls first, cat3 nulls first

OUTPUT

cat1 cat2 cat3 val
A           15
A   a       10
A   a   aa  4
A   a   ab  6
A   b       5
A   b   ba  4
A   b   bb  1
B           21
B   c       12
B   c   ca  6
B   c   cb  6
B   d       9
B   d   da  9

If you prefer underscore than null use NVL

select cat1, nvl(cat2,'_') as cat2, nvl(cat3, '_') as cat3, sum(val)
  from t1 join t2 on t1.f_id = t2.f_id
group by grouping sets ((cat1),(cat1, cat2),(cat1, cat2, cat3))
order by cat1, cat2 nulls first, cat3 nulls first

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