Comparing two files which have different number of columns

There are two files file1.txt and file2.txt that file1.txt has two columns contents and file2.txt has 3 columns contents.

file1.txt

abc,1
cba,2

file2.txt
1,abc,001
2,cba,002 

4,haifzhan,003





To get the common lines of those two files, execute this command:

awk -F',' 'NR==FNR{a[$1, $2]++;next} (a[$2,$1])' file1.txt file2.txt  > comm.txt

the output is written into comm.txt, you can see the output below contains 3 columns, that's because once common parts are found, it will output the info based upon the second input file that is file2.txt.
1,abc,001
2,cba,002



It gets the 1st column and 2nd column of file1.txt and 2nd column and 1st column of file2, and checks the equality of those fileds.file1.txt and file2.txt donot have to be sorted when execute the above commands.