Sum multiple columns using a subquery - sql

Question

I'm trying to play with Oracle's DB.
I'm trying to sum two columns from the same row and output a total on the fly.
However, I can't seem to get it to work. Here's the code I have so far.
SELECT a.name , SUM(b.sequence + b.length) as total
FROM (
SELECT a.name, a.sequence, b.length
FROM tbl1 a, tbl2 b
WHERE b.sequence = a.sequence
AND a.loc <> -1
AND a.id='10201'
ORDER BY a.location
)
The inner query works, but I can't seem to make the new query and the subquery work together.
Here's a sample table I'm using:
...[name][sequence][length]...
...['aa']['100000']['2000']...
...
...['za']['200000']['3001']...
And here's the output I'd like:
[name][ total ]
['aa']['102000']
...
['za']['203001']
Help much appreciated, thanks!

Answer 1

SUM() sums number across rows. Instead replace it with sequence + length.
...or if there is the possibility of NULL values occurring in either the sequence or length columns, use: COALESCE(sequence, 0) + COALESCE(length, 0).
Or, if your intention was indeed to produce a running total (i.e. aggregating the sum of all the totals and lengths for each user), add a GROUP BY a.name after the end of the subquery.
BTW: you shouldn't be referencing the internal aliases used inside a subquery from outside of that subquery. Some DB servers allow it (and I don't have convenient access to an Oracle server right now, so I can test it), but it's not really good practice.
I think what you are after is something like:
SELECT a.name,
SUM(B.sequence + B.length) AS total
FROM Tbl1 A
INNER JOIN Tbl2 B
ON B.sequence = A.sequence
WHERE A.loc <> -1
AND A.id = 10201
GROUP BY a.name
ORDER BY A.location

Answer 2

Your query with the subquery fails for several reasons:
You use the table alias a, but it is not defined.
You use the table alias b, but it is not defined.
You have a sum() in the select clause with unaggregated columns, but no group by.
In addition, you have an order by in the subquery which is allowed syntactically, but ignored.
Here is a better way to write the query without a subquery:
SELECT t1.name, (t1.sequence + t2.length) as total
FROM tbl1 t1 join
tbl2 t2
on t1.sequence = t2.sequence
where t1.loc <> -1 AND t1.id = '10201'
ORDER BY t1.location;
Note the use of proper join syntax, the use of aliases that make sense, and the simple calculation at this level.
Here is a version with a subquery:
select name, (sequence + length) as total
from (SELECT t1.name, t1.sequence, t2.length
FROM tbl1 t1 join
tbl2 t2
on t1.sequence = t2.sequence
where t1.loc <> -1 AND t1.id = '10201'
) t
ORDER BY location;
Note that the order by is going at the outer level. And, I gave the subquery an alias. This is not strictly required, but typically a good idea.