遇到这样一个需求，有一张表，要给这张表新增一个字段delta，delta的值等于每行的c1列的值减去上一行c1列的值。
我的解决方案，可以通过python的pandas的diff来实现，也可以通过sql来实现，如下
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import pandas as pd
srcTable = 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)
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出来的效果如下：
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tid ts1 ts2
0 1 1500443161000 1500443161240
1 1 1500443162000 1500443162994
2 1 1500443163000 1500443163067
3 1 1500443164000 1500443164993
deltaTs1 deltaTs2 delay
0 0.0 0.0 0.0
1 1000.0 1754.0 754.0
2 1000.0 73.0 -927.0
3 1000.0 1926.0 926.0
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若是用sql语句，我用的是mysql，自己构造行号rn
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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) main
left 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 |
+------+---------------+----------+---------------+----------+
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测试数据如下
pos1.csv
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1,1500443161000,1500443161240
1,1500443162000,1500443162994
1,1500443163000,1500443163067
1,1500443164000,1500443164993
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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);
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貌似有些数据库有这种当前行减去上一行数据的函数，具体我没有研究过。有知道的朋友可以告诉我一下，我印象中像Sqlserver好像有。
原文链接：https://blog.csdn.net/tulinying/article/details/75381886