rendered paste bodythis is a table named churn
sales_reg | no_of_mon | sum
-----------+-----------+-------
1006 | 1 | 646
1006 | 2 | 575
1006 | 3 | 517
1006 | 4 | 494
1006 | 5 | 463
1007 | 1 | 896
1007 | 2 | 852
1007 | 3 | 793
1007 | 4 | 751
1007 | 5 | 697
1008 | 1 | 762
1008 | 2 | 720
1008 | 3 | 693
1008 | 4 | 665
1008 | 5 | 611
2222 | 1 | 5193
2222 | 2 | 4945
2222 | 3 | 4593
2222 | 4 | 4316
2222 | 5 | 4125
4444 | 1 | 4184
4444 | 2 | 4027
4444 | 3 | 3862
4444 | 4 | 3735
4444 | 5 | 3644
in this table i need add column called "value" and the data for the value is column "sum" 0f region for month 2 - month 1
ie
for 1006
value = (646-575) 71
pls help me