In SQL, EXCEPT returns those tuples that are returned by the first SELECT operation, and not returned by the second SELECT operation.
This is the same as using a subtract operator in relational algebra.
Say we have two relations, Students and TA (Teaching Assistant). We want to return all those students who are not teaching assistants. The query can be formulated as:
SELECT Name FROM Students EXCEPT SELECT NAME FROM TA;
Rohan Mansi Megha
To retain duplicates, we must explicitly write EXCEPTALL instead of EXCEPT.
SELECT Name FROM Students EXCEPTALL SELECT Name FROM TA;
Rohan Mansi Mansi Megha
Difference between EXCEPT and NOT IN Clause
EXCEPT automatically removes all duplicates in the final result, whereas NOT IN retains duplicate tuples. It is also important to note that EXCEPT is not supported by MySQL.
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