Hi. I really need help to solve this problem.

I have few thousand data in 4 columns as below. Is there's anyway I can use excel formula to find the differences.

If ID1 match with ID2, than COURSE1 must match COURSE2.
If COURSE1 not match with COURSE2, than it will return 'error' in ERROR column.

Let say for ID1 .... 111 is abc, but in course2 its listed jkl...than error message will appeared.

ID1.........course1..........ID2............course 2
111.........abc................444............jkl
222.........def................555............abc
333.........ghi................111............jkl
444.........jkl.................222............def
555.........abc................333...........ghi

My friend suggest to do sorting and check the difference row by row. But, it will take so much time to check for thousands of data.

Hope you understand my explanation. Thanks in advanced.