While-loop - iterative control, PL-SQL Programming

Assignment Help:

WHILE-LOOP

The WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown:

WHILE condition LOOP
sequence_of_statements
END 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:

LOOP
sequence_of_statements
EXIT 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 LOOP
sequence_of_statements
done := 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;


Related Discussions:- While-loop - iterative control

Authorisations - privileges, Authorisations - Privileges As relational...

Authorisations - Privileges As relational theory is silent on the issue of authorisation, it offers nothing with which SQL's vast edifice in support of what it calls privilege

Join and and in sql, JOIN and AND in SQL In this Section is all about ...

JOIN and AND in SQL In this Section is all about one operator, JOIN. SQL's closest counterpart, NATURAL JOIN, has already been covered. Here we look at several other "join" op

Sql, Write a cursor to open an employee database and fetch the employee rec...

Write a cursor to open an employee database and fetch the employee record whose age is greater than 45

Begin parameter description in pl sql, BEGIN Parameter Description in pl sq...

BEGIN Parameter Description in pl sql: BEGIN: This keyword signals the beginning of the executable section of a PL/SQL block, that contains executable statements. The execut

Best practices/Data Warhousing, What are 3 good practices of modeling and/o...

What are 3 good practices of modeling and/or implementing data warehouses?

Implicit cursor attributes, Implicit Cursor Attributes The Implicit cur...

Implicit Cursor Attributes The Implicit cursor attributes returns the information about the execution of an INSERT, DELETE, UPDATE, or SELECT INTO statement. The cursor attribu

I need a ppd-cpa or filesharing site, PPD , CPA, Filesharing Site Projec...

PPD , CPA, Filesharing Site Project Description: This is very easy I need a PPD , CPA, Filesharing Site. [PPD] stands for (pay per download) example hotsharecash [Files

Execute privilege, EXECUTE Privilege To call an invoker-rights routine ...

EXECUTE Privilege To call an invoker-rights routine straightforwardly, the users should have the EXECUTE privilege on that routine. By yielding the privilege, you permit a user

Boolean values-assignments in pl/sql, Boolean Values Only the values TRU...

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

Using lock table, Using LOCK TABLE You use the LOCK TABLE statement to...

Using LOCK TABLE You use the LOCK TABLE statement to lock the whole database tables in the specified lock mode so that you can share or deny the access to them. For illustrati

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd