find unmatched rows
I wanted to create a query that would return the reverse inverse of two sets, where the sets are defined using multiple where clauses restricting columns. The idea was to compare the set of all possible employee days in a given month with actual entries of time on each day, and find the unmatched rows. Because SQL server doesn’t support the EXCEPT keyword, I had to figure out how to do it using traditional SQL. May be useful, since it is easy for people to understand but not that obvious how to get a computer to do it.
Here is the resulting query itself:
According to the link below, this is implemented on Oracle as the MINUS keyword.