遇到這樣一個需求，有一張表，要給這張表新增一個字段delta，delta的值等于每行的c1列的值減去上一行c1列的值。

我的解決方案，可以通過python的pandas的diff來實現，也可以通過sql來實現，如下

import pandas as pdsrcTable = pd.read_csv('pos1.csv')print(srcTable)destTable = srcTable.loc[srcTable.tid == 1, ['ts1', 'ts2']].sort_values(by='ts1')destTable.columns = ['deltaTs1', 'deltaTs2']destTable = destTable.diff()destTable = destTable.fillna(0)destTable['delay'] = destTable['deltaTs2'] - destTable['deltaTs1']print(destTable)

出來的效果如下：

 tid   ts1   ts20 1 1500443161000 15004431612401 1 1500443162000 15004431629942 1 1500443163000 15004431630673 1 1500443164000 1500443164993 deltaTs1 deltaTs2 delay0  0.0  0.0 0.01 1000.0 1754.0 754.02 1000.0  73.0 -927.03 1000.0 1926.0 926.0

若是用sql語句，我用的是mysql，自己構造行號rn

mysql> select main.t_id,main.ts1,ifnull(main.ts1-sub.ts1,0) deltaTs1,main.ts2,ifnull(main.ts2-sub.ts2,0) deltaTs2 from(SELECT t_id,ts1,ts2,(@r1 :=@r1 + 1) rn FROM pos1,(SELECT @r1 := 0) r where t_id=1 ORDER BY ts1) mainleft join (SELECT t_id,ts1,ts2,(@r2 :=@r2 + 1) rn FROM pos1,(SELECT @r2 := 0) r where t_id=1 ORDER BY ts1) sub on main.rn-1=sub.rn;+------+---------------+----------+---------------+----------+| t_id | ts1   | deltaTs1 | ts2   | deltaTs2 |+------+---------------+----------+---------------+----------+| 1 | 1500443161000 |  0 | 1500443161240 |  0 || 1 | 1500443162000 |  1000 | 1500443162994 |  1754 || 1 | 1500443163000 |  1000 | 1500443163067 |  73 || 1 | 1500443164000 |  1000 | 1500443164993 |  1926 |+------+---------------+----------+---------------+----------+

測試數據如下

pos1.csv

1,1500443161000,15004431612401,1500443162000,15004431629941,1500443163000,15004431630671,1500443164000,1500443164993

CREATE TABLE `pos1` ( `t_id` int(11) DEFAULT NULL, `ts1` bigint(22) DEFAULT NULL, `ts2` bigint(22) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8;INSERT INTO pos1 VALUES (1, 1500443161000, 1500443161240);INSERT INTO pos1 VALUES (1, 1500443162000, 1500443162994);INSERT INTO pos1 VALUES (1, 1500443163000, 1500443163067);INSERT INTO pos1 VALUES (1, 1500443164000, 1500443164993);

貌似有些數據庫有這種當前行減去上一行數據的函數，具體我沒有研究過。有知道的朋友可以告訴我一下，我印象中像Sqlserver好像有。