用于显示"总计"列更改的SQL查询

Question

我有一张包含股票交易的表格:

+------+----------------------+------------------+
| Item | Running Stock Total  | Transaction Time |
+------+----------------------+------------------+
| foo  | 4                    | 2012-05-12 11:07 |
| bar  | 3                    | 2012-05-12 10:42 |
| bar  | 3                    | 2012-05-12 9:42  |
| bar  | 2                    | 2012-05-11 15:42 |
| foo  | 3                    | 2012-05-11 10:02 |
| bar  | 3                    | 2012-05-10 13:44 |
...etc...
+------+----------------------+------------------+

即任何时候发生库存事件,在此表中创建一行 - 这可能意味着库存水平上升(订购新库存),下降(库存销售)或保持不变(库存重新定位).

我需要创建一个sql查询,该查询仅返回特定部分的库存级别实际更改的行,并且需要在"库存增加"和"库存减少"列中显示更改.

即1 Item='bar'

+------+-----------+------------+----------------------+------------------+
| Item | Stock Up  | Stock Down | Running Stock Total  | Transaction Time |
+------+-----------+------------+----------------------+------------------+
| bar  |      1    |     0      |  3                   | 2012-05-12 9:42  |
| bar  |      0    |     1      |  2                   | 2012-05-11 15:42 |
| bar  |      1    |     0      |  3                   | 2012-05-10 13:44 |
+------+-----------+------------+----------------------+------------------+

EG2 Item='foo'

+------+-----------+------------+----------------------+------------------+
| Item | Stock Up  | Stock Down | Running Stock Total  | Transaction Time |
+------+-----------+------------+----------------------+------------------+
| foo  |      1    |     0      |  4                   | 2012-05-12 11:07 |
| foo  |      2    |     0      |  3                   | 2012-05-11 10:02 |
+------+-----------+------------+----------------------+------------------+

所以像......

SELECT 
  Item, {xyz} as 'Stock Up', {abc} as 'Stock Down',  `Running Stock Total`, `Transaction Time`
FROM
  `StockTransactions`
WHERE
  `Item`='foo'
HAVING 
  ('Stock Up'>0 or 'Stock Down'>0)

可以这样做吗？

Answer 1

SELECT   `Item`,
         `Stock Up`,
         `Stock Down`,
         `Running Stock Total`,
         `Transaction Time`

FROM (
  SELECT   `Item`,
           GREATEST(`Running Stock Total` - @`last_total`, 0) AS `Stock Up`,
           GREATEST(@`last_total` - `Running Stock Total`, 0) AS `Stock Down`,
           `Running Stock Total`,
           `Transaction Time`,
           @`last_total` := `Running Stock Total`
  FROM     `StockTransactions` JOIN (SELECT @`last_total` := 0) AS lt
  WHERE    `Item` = 'bar'
  ORDER BY `Transaction Time` ASC
) AS t

ORDER BY `Transaction Time` DESC

在sqlfiddle上查看它。如果您愿意按照事务时间的升序对结果进行排序并使用额外的列，那么显然可以省略外部查询last_total。