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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;
CHECK Constraints in SQL A CHECK constraint is a table constraint defined using the key word CHECK, as already illustrated in several examples in this chapter. In particular,
Boolean Values Only the values TRUE, FALSE, & NULL can be assigned to a Boolean variable. For illustration, given the declaration DECLARE done BOOLEAN; the following statements
Effects of NULL for union - SQL The treatment of NULL in invocations of EXCEPT is as for UNION. This is different from its treatment in those of NOT IN and quantified compari
Using FOR UPDATE If you declare a cursor which will be referenced in the CURRENT OF clause of an UPDATE or DELETE statement, you should use the FOR UPDATE clause to obtain an
1. a. Write a trigger that fires when a part's price is updated. The trigger will write a record into a table called PriceUpdates. The record should contain the information of
Literature review
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UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,
Example of COALESCE operator Example: Give the total of marks for each exam (simplified solution) SELECT CourseId, COALESCE ((SELECT SUM (Mark) FROM EXAM_MARK AS EM
Assignment Statement: The assignment statement sets the present value of the variable, parameter, field, or element. The statement consists of an assignment target followed by
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