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Use of COUNT in SQL
It describes and discusses various general methods of expressing constraints, eventually noting that support for "=" with relation operands is sufficient for completeness. It also notes that every constraint can be expressed as an invocation of IS_EMPTY, where IS_EMPTY(r) is equivalent to r { } = TABLE_DUM. First, though, it gives Example, showing how to use COUNT to test a relation for emptiness. Example here is a direct translation of that one into SQL.
Example: Testing for absence of counterexamples.
CREATE ASSERTION Must_be_enrolled_to_take_exam
CHECK ((SELECT COUNT (*)
FROM EXAM_MARK
WHERE (Student_Id, CourseId ) NOT IN
(SELECT Student_Id, CourseId
FROM IS_ENROLLED_ON ) )
= 0);
Collection Methods: The collection method is a built-in function or procedure which operates on the collections and is called using the dot notation. The methods like the C
%ROWCOUNT When its cursor or cursor variable is opened, the %ROWCOUNT is zeroed. Before the first fetch, the %ROWCOUNT yields 0. Afterward, it yields the number of rows fetche
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