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

Packaging cursors, Packaging Cursors   You can split a cursor specific...

Packaging Cursors   You can split a cursor specification from its body for placement in a package. In that way, you can change the cursor body without changing the cursor spec

Pass the nulls to a dynamic sql, Pass the nulls to a dynamic SQL: Pas...

Pass the nulls to a dynamic SQL: Passing Nulls: Assume that you want to pass the nulls to a dynamic SQL statement. For illustration, you may write the EXECUTE IMMEDIATE

Order of evaluation-pl/sql expressions , Order of Evaluation When you do...

Order of Evaluation When you do not use the parentheses to specify the order of evaluation, the operator precedence determine the order. Now compare the expressions below: NOT

Sql query on hospital database, Perform the following queries on the Hospit...

Perform the following queries on the Hospital1.DB using SQL Anywhere (START EARLY!). a. Which patients have purchased the drug "Tylenol"? List the names and addresses. Arrange the

Recursive subprograms, Recursive Subprograms The recursive subprogram ...

Recursive Subprograms The recursive subprogram is the one that calls itself. Think of a recursive call as a call to a few other subprograms that does the similar task as your

Fetch statement - syntax, FETCH Statement The FETCH statement retrieve ...

FETCH Statement The FETCH statement retrieve rows of data one at a time from the result set of the multi-row query. The data is stored in fields or variables which correspond t

Cursor attributes in dynamic sql - pl sql, Using Cursor Attributes: Ev...

Using Cursor Attributes: Every cursor has 4 attributes: %NOTFOUND, %FOUND, %ISOPEN, and %ROWCOUNT. If appended to the cursor name, they return the helpful information about

Aggregate assignment-declarations in sql, Aggregate Assignment The %ROWT...

Aggregate Assignment The %ROWTYPE declaration cannot include an initialization clause. Though, there are two ways to assign values to all fields in a record at once. At First, t

Data abstraction, Data Abstraction The Data abstraction extracts the im...

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

Calculate days between ordering and shipping, An analyst in the quality ass...

An analyst in the quality assurance office reviews the time lapse between receiving an order and shipping an order. Any orders that have not been shipped within a day of the order

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