Create a new column for table B based on information from table A - sql

Question

I have this problem. I want to create a report that keeps everything in table B, but adds another column from table A (QtyRecv).
Condition: If RunningTotalQtyUsed (from table B) < QtyRecv, take that QtyRecv for the new column.
For example, for item A1, (RunningTotalQtyUsed) 55 < 100 (QtyRecv), -> ExpectedQtyRecv = 100.
But if RunningTotalQtyUsed exceeds QtyRecv, we take the next QtyRecv to cover that used quantity.
For example, 101 > 100, -> ExpectedQtyRecv = 138.
149 (RunningTotalQtyUsed) < (100 + 138) (QtyRecv) -> get 138.
250 < (100 + 138 + 121) -> get 121.
The same logic applies to item A2.
If total QtyRecv = 6 + 4 + 10 = 20, but RunningTotalQtyUsed = 31 -> result should be 99999 to notify an error that QtyRecv can't cover QtyUsed.
Table A:
Item QtyRecv
A1 100
A1 138
A1 121
A2 6
A2 4
A2 10
Table B:
Item RunningTotalQtyUsed
A1 55
A1 101
A1 149
A1 250
A2 1
A2 5
A2 9
A2 19
A2 31
Expected result:
Item RunningTotalQtyUsed ExpectedQtyRecv
A1 55 100
A1 101 138
A1 149 138
A1 250 121
A2 1 6
A2 5 6
A2 9 4
A2 19 10
A2 31 99999
What I made an effort:
SELECT b.*
FROM tableB b LEFT JOIN tableA a
ON b.item = a.item
item RunningTotalQtyUsed
A1 55
A1 55
A1 55
A1 101
A1 101
A1 101
A1 149
A1 149
A1 149
A1 250
A1 250
A1 250
A2 1
A2 1
A2 1
A2 5
A2 5
A2 5
A2 9
A2 9
A2 9
A2 19
A2 19
A2 19
A2 31
A2 31
A2 31
It doesn't keep the same number of rows as table B. How to still keep table B but add the ExpectQtyRecv from table A? Thank you so much for all the help!

Answer 1

SELECT B.TOTAL,B.SUM_RunningTotalQtyUsed,A.SUM_QtyRecv FROM
(
SELECT B.ITEM,SUM(B.RunningTotalQtyUsed)AS SUM_RunningTotalQtyUsed
FROM TABLE_B AS B
GROUP BY B.ITEM
)B_TOTAL
LEFT JOIN
(
SELECT A.ITEM,SUM(A.QtyRecv)AS SUM_QtyRecv
FROM TABLE_A AS A
GROUP BY A.ITEM
)A_TOTAL ON B.ITEM=A.ITEM
I can not be sure, but may be you need something like above ?