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Recursion versus Iteration
Dissimilar the iteration, recursion is not crucial to PL/SQL programming. Any problem which can be solved using recursion can be solving using the iteration. Also, the iterative version of the subprogram is typically easier to design than the recursive version. Though, the recursive version is typically simpler, smaller, and hence easier to debug. Compare the functions below that calculate the nth Fibonacci number:
-- recursive version
FUNCTION fib (n POSITIVE) RETURN INTEGER IS
BEGIN
IF (n = 1) OR (n = 2) THEN
RETURN 1;
ELSE
RETURN fib(n - 1) + fib(n - 2);
END IF;
END fib;
-- iterative version
pos1 INTEGER := 1;
pos2 INTEGER := 0;
cum INTEGER;
cum := pos1 + pos2;
FOR i IN 3..n LOOP
pos2 := pos1;
pos1 := cum;
END LOOP;
RETURN cum;
The recursive version of the Fibonacci is more graceful than the iterative version. Though, the iterative version is more accurate; it runs faster and uses less storage. That is as each recursive call needs an additional time and memory. As the number of recursive calls gets bigger, so does the difference in effectiveness. Still, if you expect the number of recursive calls to be little, you may choose the recursive version for its readability.
Declaring Subprograms You can declare subprograms in any PL/SQL subprogram, block, or package. But, you should declare subprograms at the end of the declarative part after a
OUT Mode An OUT parameter returns values to the caller of a subprogram. Within the subprogram, an OUT parameter act like a variable. That means that you can use an OUT formal
Important Distinctions The list of important distinctions are given below: Value versus variable Syntax versus semantics Variable versus variable reference
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
IN Mode An IN parameter pass the values to the subprogram being called. Within the subprogram, an IN parameter acts like a constant. And hence, it cannot be assigned a value.
Use the PLS_INTEGER Datatype When you require to declare an integer variable, use the datatype PLS_INTEGER that is the most efficient numeric type. That is as the PLS_INTEGER
Using Operator DEREF: You cannot navigate through refs within the PL/SQL procedural statements. Rather than, you should use the operator DEREF in the SQL statement. The DEREF
Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (
Data Types in SQL - Character CHARACTER or, synonymously, CHAR, for character strings. When this type is to be the declared type of something (e.g., a column), the permissible
First Step at defining type SID in SQL CREATE TYPE SID AS ( C VARCHAR(5) ) ; Explanation: TYPE SID announces that a type named SID is being defined to the syst
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