You can probably see by this point how the pieces are coming together: each time frame has a starting point and an ending point. If there were no overlap at all, we’d see in the fourth column a number followed by a NULL, followed by a number followed by a NULL, etc. But we clearly don’t see that: we see work item ordinals 3 and 4 share some overlap: item 3 started at 3:06:15 PM and ended after item 4’s start of 3:07:20 PM. This means that those two overlapped to some extent. Then we see two NULL values, which means they both ended before 5 began. So far so good for our developers!
Click through for a bunch of T-SQL scripts, images, and important advice about always having interns around to take the blame.