mysql – 用于显示“总计”列更改的SQL查询

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项=’酒吧’

+------+-----------+------------+----------------------+------------------+
| 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 |
+------+-----------+------------+----------------------+------------------+

例如2项=’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？

最佳答案

SELECT   `Item`,`Stock Up`,`Stock Down`,`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`,`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.如果您对按交易时间的升序和额外的last_total列排序的结果感到满意,则显然可以省略外部查询.