File: A tuple (student_id, duty_id, true) should only occur once
Unfortunately, as of today, there are 4 tuples violating this requirement in our instance:
duty_id | student_id | count ---------+------------+------- 1 | 30 | 2 79 | 98 | 2 79 | 253 | 2 79 | 250 | 2
The corresponding bug should be identified and the database should implement checks.