How to return the same SUM value from two tables

Question

Hello,
I have the following data:
SQL> SELECT * FROM t1;
     T1_ID   T1_VALUE
         1        500
         1        500
SQL> SELECT * FROM t2;
     T2_ID   T2_VALUE
         1       1000
SQL> SELECT t1_id, SUM(t1_value), SUM(t2_value)
  2    FROM t1, t2
  3   WHERE t1_id = t2_id
  4   GROUP BY t1_id;
     T1_ID SUM(T1_VALUE) SUM(T2_VALUE)
         1          1000          2000How is it possible that SUM(T2_VALUE) returns also 1000.
Thank you

Answer 1

Here's one way:
with t1 as (select 1 t1_id, 500 t1_value from dual union all
            select 1 t1_id, 500 t1_value from dual),
     t2 as (select 1 t2_id, 1000 t2_value from dual)
select t3.t3_id, t3.t3_sum, t4.t4_sum
from   (select t1_id t3_id, sum(t1_value) t3_sum from t1
        group by t1_id) t3,
       (select t2_id t4_id, sum(t2_value) t4_sum from t2
        group by t2_id) t4
where  t3.t3_id = t4.t4_id