st:how to keep the overlapping variables as many as possible when combining data sets

[Amanda Fu <mandy.fu1@gmail.com>]

Dear Statalisters,

I was trying to use "merge" to combine the following two data sets:

data set 1: (master data set)
------------------------
id	v1       	v2
1	12     	b
2	45    	5
3		
4	111  	r
5	144     	c
-----------------------
data set 2: (using data set) , where v1 and v2 are overlapped with
comparison to data set 1.
-----------------------
id	v1    	v2	v3
1	12           m	8
2	45         		8
3	78      	0	8
4	111     	2	8
5	          	3	
6	8	         	7
----------------------------
The following data set is what I want to see after the combination. That is:
When there are overlapping variables, if the values in the master data
set is available, the one in the master data set is used. On the
condition that the value in the master data set is missing, use the
one in the using data set if it is available.
----------------------------goal data set
id	v1    	v2	v3
1	12            b	8
2	45         	5	8
3	78      	0	8
4	111     	r	8
5	144         c 		
6	8	        	7
----------------------------
But when I tried to use ---merge id using "2"----, the result is that
for the overlapping variables only the values in the master data set
are kept as following:
----------------------------merged data set
id	v1    	v2	v3
1	12            b	8
2	45         	5	8
3	         		8
4	111     	r	8
5	144         c 		
6	8	        	7
----------------------------
May I know how I can get the goal data set using merge? Thanks for your time!

Best wishes,
Amanda Fu
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