There is a table full of grouped values like the following
nodeid link_type primary
11 outflowlink 1
11 inflowlink 1
11 outflowlink 2
Primary of 1 indicates a primary water course. Primary of 2 indicates a secondary water course.
Obviously, one of the out flow links is an error, as its primacy value is 2. It is wrong that water flows from a primary water course into a secondary water course.
How can a function can be designed to find and report such errors?