Q:

Prevent duplicate row values

I've done some digging and I can't find an effective way to prevent duplicate entries based on my needs.  I need columns 2 (proj_id) and column 4 (dept_id) never to be the same, as each dept would only work on a project once.  So, rows 1 and 4, 6 and 7, and 14 and 15 shouldn't be allowed.  I'll keep digging as well.
summary_id  proj_id     hours_id    dept_id     date_entered
1   8   3   6   9/9/2012
2   2   2   6   9/9/2012
3   1   6   19  9/9/2012
4   8   3   6   9/9/2012
5   2   5   17  9/9/2012
6   7   2   5   9/9/2012
7   7   2   5   9/9/2012
8   2   5   17  9/9/2012
9   7   4   17  10/10/2012
10  3   6   1   10/10/2012
11  5   1   15  10/10/2012
12  4   4   3   10/10/2012
13  3   5   1   10/10/2012
14  8   2   13  10/10/2012
15  8   2   13  10/10/2012

A:

Before applying unique combine key to your table, you have to remove duplicate records first then apply the following sql command: 
ALTER TABLE your_table_name ADD UNIQUE (proj_id, dept_id);

