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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.
Use Object Types and Collections The Collection types and object types increase your efficiency by allowing for the realistic data modeling. The Complex real-world entities an
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,
Predefined Exceptions The internal exception is raised implicitly whenever your PL/SQL program exceeds a system-dependent limit or violates an Oracle rule. Each & every Oracle
Stored Subprograms Normally, tools (like Oracle Forms) which incorporate the PL/SQL engine can store subprograms locally for later, strictly local execution. Though, to become
MAX and MIN operator in SQL Example: (SELECT MAX (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') (SELECT MIN (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') Example
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
Parameter SELF in pl/sql The MEMBER methods recognize a built-in parameter named SELF that is an instance of the object type. Whether declared explicitly or implicitly, it is
Example of GROUPBY Operator Example: How many students sat each exam, using GROUP BY, NATURAL LEFT JOIN, and COALESCE SELECT CourseId, COALESCE (n, 0) AS n FROM COURS
Using a Join on 2 tables, select all columns and all rows from the tables without the use of a Cartesian product. Query: SELECT * FROM EMPLOYEE1 JOIN CONTRACT ON EMPLOYEE
Problem: (a) Define the following terms: (i) data mining. (ii) OLAP. (b) Differentiate between snowflake schema and star schema. Support your answer with appropriate
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