Awk comparison on files

Question

I have 2 files:

file1:

1,apple  
2,mango  
3,banana  
44,orange  

file2:

1,apple  
22,  
31,xyz  
2,man  
3,banana  
44,oran   
44,orange

I need to find the differences from both the files using column 1 and checking column 2. I don't want to use $0 as its printing the lines which of 1st file which are not present in file 2 too.

result output should be printed in file3 as :

2,mango,man  

as of now in other question, I asked and got an answer as:-

   { awk 'BEGIN{FS=OFS=","}($1 in a) && a[$1]!=$2{print $1,a[$1],$2}{a[$1]=$2}' file1 file2 >> file3 }

the issue with this solution is that its printing wrong entries in file 3 due to duplicates present in file 2 (for column 1).
I need to write these duplicates in file 4 and should not be reflected in file3.

Answer 1

For joining files based on unique records from file 2

join -t',' <(sort -t',' -k1 file1) <(sort -t',' -n -k1 -u file2) | awk -F',' '{if($2!=$3) print}'

For finding duplicate entry in file2

awk -F',' 'seen[$1]++

Demo :

$man uniq 
$cat fil*
1,apple  
2,mango  
3,banana  
44,orange
1,apple  
22,  
31,xyz  
2,man  
3,banana  
44,oran   
44,orange
$join -t','  <(sort -t',' -k1 file1) <(sort -t',' -n -k1 -u  file2)  | awk -F',' '{if($2!=$3) print}'
2,mango  ,man  
44,orange,oran   
$

$awk -F',' 'seen[$1]++' file2
44,orange
$