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Short-Circuit Evaluation When computing a logical expression, the PL/SQL uses short-circuit evaluation. That is, the PL/SQL stops computing the expression as soon as the result can be determined. This permits you to write the expressions that might otherwise cause an error. Now consider the following OR expression:DECLARE...on_hand INTEGER;on_order INTEGER;BEGIN..IF (on_hand = 0) OR ((on_order / on_hand) < 5) THEN...END IF;END;Whenever the value of on_hand is zero, the left operand yields TRUE, so the PL/SQL require not compute the right operand. If PL/SQL were to compute both operands before applying the OR operator, the right operand would cause a division by the zero error. In any case, it is a poor programming practice to rely on the short-circuit computation.
Procedural Constraint Enforcement (Triggers) SQL has an alternative method of addressing database integrity, involving event-driven procedural code. The special procedures th
1.( /5 marks) Suppose that a B+-tree index with the search key (dept_name, building) is available on relation department. What would be the best way to handle the following selecti
UNION and OR - SQL SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, su
Using %ROWTYPE The %ROWTYPE attribute gives a record type which represents a row in a table (or view). The record can store the whole row of data selected from the table or fetc
#quesWrite a cursor to open an employee database and fetch the employee record whose age is greater than 45.tion..
Using SET TRANSACTION You use the SET TRANSACTION statement to begin the read-only or read-write transaction, start an isolation level, or assign your present transaction to a
Advantages of PL/SQL The PL/SQL is a high-performance transaction processing, completely portable language that offers the following advantages as shown: 1) Support for SQL
Restriction in SQL Syntax: SELECT DISTINCT StudentId FROM IS_CALLED WHERE Name = 'Boris' The WHERE clause operates on the result of the FROM clause in analogo
UNION ALL - SQL Further varieties of UNION arise when we replace the key word DISTINCT by ALL in any of the foregoing examples, as in Example. ALL specifies that if row r appe
Deleting Objects You can use the DELETE statement to eradicate objects from an object table. To eradicate objects selectively, you use the WHERE clause, as shown below: BEG
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