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Example of EXCEPT Operator - SQL
Example, like its counterpart in the theory book, illustrates the convenience of allowing any table expression to be the source for an INSERT. It assumes that all the exam scripts submitted by students have been marked and it has been decided to record marks of zero for students who failed to turn up for an exam they should have sat. (Remember that SQL's EXCEPT requires its operands to be of the same degree, unlike NOT MATCHING-hence the third element, 0, of the second operand in the example.)
Example: Awarding zero marks to students who failed to take the exam
INSERT INTO EXAM_MARK
SELECT StudentId, CourseId, 0
FROM IS_ENROLLED_ON
EXCEPT
FROM EXAM_MARK;
Example of Null operator - NiNo Rule If we wanted to make HIGHER_OF adhere to "NULL in, NULL out"-let's call it the NiNo rule-we would have to write something like what is sho
Example of Foreign Key Constraint Example: Alternative formulation for 6.3 as a foreign key constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_take_exam
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Comparison Operators Usually, you use the comparison operators in the WHERE clause of a data manipulation statement to form the predicates, that compare one expression to anot
Error Handling The PL/SQL makes it easy to detect and process the predefined and user-defined error conditions known as exceptions. Whenever an error occurs, an exception is ra
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Semidifference and NOT - SQL In this section first describe the relational difference operator, named MINUS. Example here shows SQL's closest counterpart of that operator.
Adding Table Constraints ALTER TABLE ENROLMENT ADD CONSTRAINT NameNotNull CHECK (Name IS NOT NULL) ; ALTER TABLE ENROLMENT ADD CONSTRAINT PK_StudentId_CourseId PRIM
Pass the nulls to a dynamic SQL: Passing Nulls: Assume that you want to pass the nulls to a dynamic SQL statement. For illustration, you may write the EXECUTE IMMEDIATE
Write a cursor to open an employee database and fetch the employee record whose age is greater than 45
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