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WHILE-LOOPThe WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown:WHILE condition LOOPsequence_of_statementsEND LOOP;Before each of the iteration of the loop, the condition is computed. If the condition is true, then the series of statements is executed, then the control resumes at the top of the loop. When the condition is false or null, the loop is then bypassed and control passes to the next statement. An illustration is shown below:WHILE total <= 25000 LOOP...SELECT sal INTO salary FROM emp WHERE...total := total + salary;END LOOP;The number of iterations depends on the condition and is not known until the loop done. The condition is tested at the top of the loop, so the series might execute zero times. In the last illustration, if the initial value of total is bigger than 25000, the condition is false and the loop is bypassed.A few languages have a LOOP UNTIL or REPEAT UNTIL structure, that tests the condition at the bottom of the loop rather than at the top. So, the sequence of the statements is executed at least once. The PL/SQL has no such structure, but you can easily build one, as shown:LOOPsequence_of_statementsEXIT WHEN boolean_expression;END LOOP;To make sure that a WHILE loop executes at least once, then use an initialized Boolean variable in the condition which is as shown below:done := FALSE;WHILE NOT done LOOPsequence_of_statementsdone := boolean_expression;END LOOP;The statement inside the loop should assign a new value to the Boolean variable. Or else, you have an infinite loop. For illustration, the following LOOP statements are logically equal:WHILE TRUE LOOP | LOOP... | ...END LOOP; | END LOOP;
Exceptions An exception is the runtime error or warning condition that can be predefined or user-defined. The Predefined exceptions are raised implicitly through runtime system
Primary Key - SQL A PRIMARY KEY specification carries an implicit NOT NULL constraint on each column of the specified key. When more than one key constraint is required, the k
Write a program to implement the inverted file shown in the slides (Simple Index file, LabelID file and Data file). Use the Avail_List to point at the deleted Label IDs so that th
Declaring Exceptions The Exceptions can be declared only in the declarative part of the PL/SQL subprogram, block, or package. By introducing its name, you can declare an excep
Redeclaring Predefined Exceptions Keep in mind that, the PL/SQL declares predefined exceptions globally in the package STANDARD; Therefore you need not declare them yourself.
EXIT-WHEN The EXIT-WHEN statement permits a loop to complete conditionally. Whenever the EXIT statement is encountered, the condition in the WHEN clause is computed. When the co
Using Operator VALUE: As you may expect, the operator VALUE returns the value of an object. The VALUE takes its argument a correlation variable. For illustration, to return a
Defining Autonomous Transactions To define an autonomous transaction, you use the pragma (compiler directive) AUTONOMOUS_TRANSACTION. The pragma instructs the PL/SQL compiler
Data Abstraction The Data abstraction extracts the important properties of data while ignoring the not necessary details. Once you design a data structure, you can fail to reme
Iterative Control: LOOP Statements The LOOP statement executes a series of statements multiple times. There are 3 forms of LOOP statements: LOOP, WHILE-LOOP, & FOR-LOOP. LOOP
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