row numbers based on conditions

  
company
txn_id
transaction_date
grp

1
A
t001
01.01.2014 00:00:00
1

2
A
t002
02.01.2014 00:00:00
1

3
A
t003
03.01.2014 00:00:00
1

4
A
t013
12.01.2014 00:00:00
4

5
B
t004
02.01.2014 00:00:00
1

6
B
t005
02.01.2014 00:00:00
1

7
B
t015
06.01.2014 00:00:00
2

8
B
t019
07.01.2014 00:00:00
2

9
B
t035
10.01.2014 00:00:00
4

10
C
t006
03.01.2014 00:00:00
1

11
C
t008
17.01.2014 00:00:00
2

12
C
t007
19.01.2014 00:00:00
2

13
C
t009
27.01.2014 00:00:00
4