同一张表中的正负值

Question

这是我的桌子形状：

---------------------------------------
ProductID   |   Reference   |   Qty   |
---------------------------------------
1           |    Plus       |    8    |
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1           |    Minus      |    2    |
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2           |    Plus       |    18   |
---------------------------------------
2           |    Minus      |    6    |
---------------------------------------
2           |    Minus      |    3    |
---------------------------------------

结果将是这样。

----------------------------
ProductID   |   Rem. Qty   |
----------------------------
1           |      6       |
----------------------------
2           |      9       |
----------------------------

Answer 1

我们可以在此处尝试使用聚合：

SELECT
    ProductID,
    SUM(CASE WHEN Reference = 'Plus' THEN Qty ELSE -1.0 * Qty END) AS Total
FROM yourTable
GROUP BY
    ProductID;