there is a file1 as below:

```
21,2018042100  
22,2018042101  
87,2018042102  
98,2018042103    

```

there is file2 as below: 

```
45,2018042100      
86,2018042102      
87,2018042103     

```

what I need is: (file3) 

```
2018042100,21,45    
2018042101,22,0         
2018042102,87,86  
2018042103,98,87

```

in row #2 in file3, data for 2018042101 is exist in file1 but it is not exist in file2. So, 0 is inserted in column $3 which is belong to file2.

kindly please assist to find out how I can create a file like file3.  

Thanks.