计算差异

Question

我有如下表

+-----+--------+-----------+-----------+-------+ 
| id | job_id | source_id | target_id | value | 
+-----+--------+-----------+-----------+-------+ 
| 204 | 5283 |  247 |  228 | 1201 | 
| 349 | 4006 |  247 |  228 | 100 | 
| 350 | 4007 |  247 |  228 | 500 | 
| 351 | 4008 |  247 |  228 | 1000 | 
| 352 | 4009 |   1 |  100 | 100 | 
| 353 | 4010 |   1 |  100 | 500 | 
| 354 | 4011 |   1 |  100 | 50 | 
+-----+--------+-----------+-----------+-------+ 

我想列值通过SOURCE_ID和target_id之间的电邮宣传创建一个差异。较旧的（较小的ID）应该与较新的一个进行比较

我已经搜索了一点点，发现​​3210。我已经写了一个小的查询，并在“一般”的作品，而不是作为expexted：

SELECT 
    c.id, c.source_id, c.target_id, c.value, COALESCE(c1.value - c.value, -1) AS diff 
FROM 
    changes c LEFT JOIN changes c1 ON (c1.source_id = c.source_id AND c1.target_id = c.target_id) 
GROUP BY c.source_id, c.target_id, c.job_id 
ORDER BY c.id 

我得到了以下结果：

+-----+-----------+-----------+-------+------+ 
| id | source_id | target_id | value | diff | 
+-----+-----------+-----------+-------+------+ 
| 204 |  247 |  228 | 1201 | 0 | 
| 349 |  247 |  228 | 100 | 1101 | 
| 350 |  247 |  228 | 500 | 701 | 
| 351 |  247 |  228 | 1000 | 201 | 
| 352 |   1 |  100 | 100 | 0 | 
| 353 |   1 |  100 | 500 | -400 | 
| 354 |   1 |  100 | 50 | 50 | 
+-----+-----------+-----------+-------+------+ 

你可以看到DIFF工作编号349和353，我希望对所有行都有如下预期结果：

+-----+-----------+-----------+-------+------+ 
| id | source_id | target_id | value | diff | 
+-----+-----------+-----------+-------+------+ 
| 204 |  247 |  228 | 1201 | 1201 | 
| 349 |  247 |  228 | 100 | 1101 | 
| 350 |  247 |  228 | 500 | -400 | 
| 351 |  247 |  228 | 1000 | -500 | 
| 352 |   1 |  100 | 100 | 100 | 
| 353 |   1 |  100 | 500 | -400 | 
| 354 |   1 |  100 | 50 | 450 | 
+-----+-----------+-----------+-------+------+ 

如果差异结果是反转的，那就没有问题了。

我错过了什么？
感谢您的任何提示。

Answer 1

如果使用用户定义的变量，你不需要参加表本身。只是做逐行comparrision像这样

SELECT 
    id, 
    job_id, 
    target_id, 
    if(@a = source_id, @b - value, value) as diff, 
    @b := value as value, 
    @a := source_id as source_id 
FROM changes 
CROSS JOIN (SELECT @a:=0, @b:=0)t 

DEMO

Answer 2

我想你想：

SELECT c.id, 
      c.source_id, 
      c.target_id, 
      c.value, 
      c.value - COALESCE(co.value, 0) delta 
    FROM changes c 
LEFT JOIN (
     SELECT ci.id, MAX(cio.id) prev_id 
     FROM changes ci 
     JOIN changes cio 
      ON cio.source_id = ci.source_id 
      AND cio.target_id = ci.target_id 
      AND cio.id < ci.id 
    GROUP BY ci.id 
     ) link 
     ON link.id = c.id 
LEFT JOIN changes co 
     ON co.id = link.prev_id 
ORDER BY c.id 

我稍微改变了逻辑。

在您预期的结果，第一DIFF已经从未知（0？）去了1201和报告为阳性差异，但第二次从1201去了100，并且还在报告为阳性。

我已经改名为增量，并给予您从先前的值移到新值所需的数量。

COALESCE(co.value-c.value, c.value) diff 

这将得到您所提供的结果（改为-500，这点我相信DIFF 500是一个错字）：很显然，如果你愿意，你可以改变这一点。

Answer 3

我怀疑你正在寻找这样的事情 - 虽然COALESCE位似乎误导我...

SELECT a.*, COALESCE(b.value-a.value,a.value) diff 
    FROM 
    (SELECT x.* , COUNT(*) rank FROM changes x JOIN changes y ON y.id <= x.id GROUP BY x.id) a 
    LEFT 
    JOIN 
    (SELECT x.* , COUNT(*) rank FROM changes x JOIN changes y ON y.id <= x.id GROUP BY x.id) b 
    ON b.source_id = a.source_id 
    AND b.rank = a.rank - 1;