Retrieve from Oracle db key value pair - oracle

Question

I need to retrieve 3 values with different key from a key value pair table.
My database schema as follows. I need to reach to table3 from table1 by taking the E_SUBID and then joining the table2 with E_SUBID. Once table1 and table2 are joined I need take to take E_CID from table2 to join it with table2 E_CID to get the "Attr_Value" keeping E_CID as a criteria.
Table1
------------------------
|E_SUBID| B_LocationID |
|1 100 |
|2 101 |
|3 102 |
Table2
-----------------
|E_CID | E_SUBID|
|10 1 |
|11 2 |
|12 3 |
Table3
---------------------------------
|E_CID | Attr_name | Attr_Value |
|10 Product Samsung |
|10 Model Smartphone |
|10 usage daily |
|11 Product Apple |
|11 Model Ipad |
|11 usage everyday |
|12 Model smartwatch |
I have been successful to join table1,table2 and table3 but I cannot get the required output which as follows
OUTPUT
|Product | Model | Usage |
Samsung Smartphone daily
Apple Ipad everyday
null smartwatch null
The query which joins table1, table2 and table3 as follows
select distinct t3.Attr_value as Product
from table1 t1, table2 t2, table3 t3
where t1.E_SUBID = t2.E_SUBID and
t2.E_CID = t3.E_CID and
t3.Attr_name=?????
order by Product;
Thank you for your time.

Answer 1

In a case like this, you can join to table3 as often as you need to for each attribute name you wish to display:
select
p.attr_value product,
m.attr_value "model", -- Quotes to escape reserved word
u.attr_value usage
from table1 t1
join table2 t2 on t1.e_subid = t2.e_subid
left outer join table3 p on t2.e_cid = p.e_cid and p.attr_name = 'Product'
left outer join table3 m on t2.e_cid = m.e_cid and m.attr_name = 'Model'
left outer join table3 u on t2.e_cid = u.e_cid and u.attr_name = 'Usage'
order by 1;
Edit
Based on the comment, by making table3 optional (outer join) the query should return all rows and whether or not a Model or Usage or Product has been defined.

Answer 2

Try as below ... Basically you are trying to transpose the rows to column in table3.
Select Product, "Model", Usage
From
(
Select
t1.E_SUBID,
t2.E_CID,
Max(Case when T3.Attr_name = 'Product' Then T3.Attr_Value else null end) Product,
max(Case when T3.Attr_name = 'Model' Then T3.Attr_Value else null end) Model,
max(Case when T3.Attr_name = 'Usage' Then T3.Attr_Value else null end) Usage
From Table1 t1,
Table2 t2,
Table3 t3
Where
t1.E_SUBID = t2.E_SUBID
and t2.E_CID = t3.E_CID
group by t1.t1.E_SUBID,t2.E_CID
);