sum of column based on distinct value of other column in Oracle - oracle

Question

Table A
A1 A2
1 7
2 8
1 9
Table B
A1 B2
1 2
2 3
i want something like this
select A.A1,sum(case when distinct A.A1 then B2),sum(A.A2) from
A,B
where A.A1=B.A1(+)
group by A.A1
After joining my table will be
A1 A2 B2
1 7 2
2 8 3
1 9 2
Resulting Table
A1 A2 B2
1 7+9 2(only once)
2 8 3
how to get sum of B2 when distinct A1 after joining the tables as stated above.
Thanks in advance

Answer 1

Use JOIN and GROUP BY.
Query
SELECT t1.A1, SUM(t1.A2) AS A1, SUM(t2.B2) AS B2
FROM TableA t1
JOIN TableB t2
ON t1.A1 = t2.A1
GROUP BY t1.A1;

Answer 2

Since table_b.a1 is unique, the best way to do this would be to work out the sum of table_a.a2 first to reduce the number of rows you're joining against, and then join to table_b. Then you don't need to worry about summing the distinct table_b.b2 values, which you would otherwise have to do.
WITH table_a AS (SELECT 1 a1, 7 a2 FROM dual UNION ALL
SELECT 2 a1, 8 a2 FROM dual UNION ALL
SELECT 1 a1, 9 a2 FROM dual),
table_b AS (SELECT 1 a1, 2 b2 FROM dual UNION ALL
SELECT 2 a1, 3 b2 FROM dual)
-- end of mimicking your two tables with sample_data in them;
-- see the sql below:
SELECT ta.a1,
ta.a2,
tb.b2
FROM (SELECT a1, SUM(a2) a2
FROM table_a
GROUP BY a1) ta
INNER JOIN table_b tb ON ta.a1 = tb.a1;
A1 A2 B2
---------- ---------- ----------
1 16 2
2 8 3
If you absolutely must join the two tables first (I don't recommend; this is making more work for the database to do), then you could do something like:
WITH table_a AS (SELECT 1 a1, 7 a2 FROM dual UNION ALL
SELECT 2 a1, 8 a2 FROM dual UNION ALL
SELECT 1 a1, 9 a2 FROM dual),
table_b AS (SELECT 1 a1, 2 b2 FROM dual UNION ALL
SELECT 2 a1, 3 b2 FROM dual)
SELECT ta.a1,
SUM(ta.a2) a2,
MAX(tb.b2) b2
FROM table_a ta
INNER JOIN table_b tb ON ta.a1 = tb.a1
GROUP BY ta.a1;
A1 A2 B2
---------- ---------- ----------
1 16 2
2 8 3
Since there can only be one distinct value for table_b.b2 per table_a.a1, we can just pick one of the values to use via MAX (we could have used MIN or SUM(distinct tb.b2) instead, fyi).