I have data like this:

tableA.ID
---------
1
2
3

tableB.ID tableB.NUM
--------------------
1         10
1         15
2         18
3         12
2         15
3         13
1         12

I need to select tableA IDs where the sum of their NUMs in tableB is above the average of all tableA IDs sums. In other words:

SUM ID=1 -> 10+15+12 = 37
SUM ID=2 -> 18+12+15 = 45
SUM ID=3 -> 12+13    = 25

AVG ALL IDs -> (37+45+25)/3 = 35

The SELECT must only show ID 1 and 2 because 37 > 35, 45 > 35 but 25 < 35.

This is my current query which is working fine:

SELECT tableA.ID
FROM tableA, tableB
WHERE tableA.ID = tableB.ID
HAVING SUM(tableB.NUM) > (
    SELECT AVG(MY_SUM)
    FROM (
        SELECT SUM(tableB.NUM) MY_SUM
        FROM tableA, tableB
        WHERE tableA.ID = tableB.ID
        GROUP BY tableA.ID
    )
)
GROUP BY tableA.ID

But I have a feeling there might be a better way without all those nested SELECTs. Perhaps 2, but 3 feels like too much. I'm probably wrong though.

For instance, why can't I do something simple like this:

SELECT tableA.ID
FROM tableA, tableB
WHERE tableA.ID = tableB.ID
HAVING SUM(tableB.NUM) > AVG(SUM(tableB.NUM))
GROUP BY tableA.ID

Or this:

SELECT tableA.ID, SUM(tableB.NUM) MY_SUM
FROM tableA, tableB
WHERE tableA.ID = tableB.ID
HAVING MY_SUM > AVG(MY_SUM)
GROUP BY tableA.ID