SQL- how to join 3 tables but only group by columns from two

Question

I am trying to join 3 tables below together but I only want to group by customer_ID In the first 2 table, how to achieve this?
In other words the third table I use is only to eliminate the records. Many thanks!

table 1

customer_ID  product_No  
 100          ABC001
 100          ABC111
 100          ABC112 
 200          ABC002

table2

product_No   Amount
 ABC001        10
 ABC002        50
 ABC111        60
 ABC112        70

table 3

Valid_Product  Desc
 ABC001         Y
 ABC111         Y

I'm ok with joining table 1 and 2 by doing

select 
    t1.product_No, Max(t2.amount)
from 
    t1, t2
where 
    t1.product_No = t2.product_No
group by 
    customer_ID

Now how do I in the same query join to table 3 and only get the value of ABC111 for customer 100 as that's the valid product with Max amount?

so the result would be Customer_ID 100 Amount 60 The goal is to get the max amount of a product (only if the product is in the 3rd table with a desc Y) under a customer.

Answer 1

If for each customer you want the valid product with the maximum amount, then use row_number() :

select *
from (select t1.*, t2.amount,
             row_number() over (partition by t1.customer_id t2.amount desc) as seqnum
      from t1 join
           t2
           on t1.product_No = t2.product_No join
           t3
           on t3.Valid_Product = t1.product_No
     ) t
where seqnum = 1;

Answer 2

It's just another join and a WHERE clause filtering on t3.desc . It doesn't seem like you need the columns from T3 in the projection.

select t1.customer_ID, Max(t2.amount)
from t1
     join t2
     on t1.product_No = t2.product_No
     join t3
     on t1.product_No = t3.valid_product
where t3.desc = 'Y'
Group by t1.customer_ID

---

Incidentally, you will notice I wrote the query using the ANSI 92 join syntax. Oracle has supported this since 9i (twenty years now) and it really does make queries easier to read.

Answer 3

For your output sample simple aggregate function and join is enough

select t1.*,t2.Amount from table1 t1 join

 (
 select * from table2 t2 where amount in
   ( 
    select max(Amount) as amt
   from table2 inner join table3 t3 on 
    t2.product_No=t3.Valid_Product

   )  
  ) t2 on t1.product_No=t2.product_No

Answer 4

You want to know whether a product exists in table 3. We check existence in SQL with EXISTS or IN .

select 
  t1.customer_id, max(t2.amount)
from t2
left join t2 on  t2.product_no = t1.product_no
where t1.product_no in (select product_no from t3 where desc = 'Y')
group by t1.customer_id
order by t1.customer_id;

Don't join, when you are only looking up a table whether an entry exists.

Answer 5

Try below using row_number()

select * from 
(select customer_ID,t1.product_No, t2.amount, row_number() over (partition by customerid order by amount desc) as rn
from t1 inner join t2
where t1.product_No = t2.product_No)a
inner join table3 on a.product_no = Valid_Product
where rn=1