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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;
Using EXTEND To enlarge the size of a collection, use EXTEND. This process has 3 forms. The EXTEND appends one null element to a collection. And the EXTEND(n) appends n null e
Comparison Operators Usually, you use the comparison operators in the WHERE clause of a data manipulation statement to form the predicates, that compare one expression to anot
PITS Depressions in secondary cell wall is called pit. A pit present on the free cell wall surface without its partner is called Blind pit. It consists of 2 parts -
IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do
Example of GROUP BY and COLLECT Operator Example: Using GROUP BY and COLLECT to obtain C_ER2 SELECT CourseId, CAST ( COLLECT (ROW (StudentId, Mark)) AS ROW (Studen
Keyword and Parameter Description: boolean_expression: This is an expression which results the Boolean value TRUE, FALSE, & NULL. It is related with a series of statement
Name Resolution In potentially uncertain SQL statements, the names of the database columns take precedence over the names of the local variables and formal parameters. For e.g.
Multiple Assignment- SQL SQL supports multiple assignment to local variables and also applies multiple assignment semantics in SET clauses of UPDATE statements, but does not
DECLARE : This keyword signals the beginning of the declarative section of the PL/SQL block, that contains local declarations. The Items declared locally exist only within the
Parameter Aliasing To optimize the subprogram call, the PL/SQL compiler can decide between the two techniques of the parameter passing. With the by-value techniques, the v
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