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Assigning and Comparing CollectionsOne collection can be assigned to other by an SELECT, INSERT, UPDATE, or FETCH statement, an assignment statement, or by a subprogram call. As the illustration shown below, the collections should have the same datatype. Having the similar element type is not enough.DECLARETYPE Clientele IS VARRAY(100) OF Customer;TYPE Vips IS VARRAY(100) OF Customer;group1 Clientele := Clientele(...);group2 Clientele := Clientele(...);group3 Vips := Vips(...);BEGINgroup2 := group1;group3 := group2; -- illegal; Various datatypes becomes automatically null (and should be reinitialized). Now consider the illustration as shown below: DECLARETYPE Clientele IS TABLE OF Customer;group1 Clientele := Clientele(...); -- initializedgroup2 Clientele; -- atomically nullBEGINIF group1 IS NULL THEN ... -- condition yields FALSEgroup1 := group2;IF group1 IS NULL THEN ... -- condition yields TRUE...END;Similarly, if you assign the non-value NULL to a collection, the collection becomes automatically null.Assigning Collection ElementsYou can assign the value of an expression to the specific element in a collection by using the syntaxcollection_name(subscript) := expression;Where the expression yields a value of the type specified for elements in the collection type definition. If the subscript is null or not convertible to an integer, the PL/SQL raises the predefined exception VALUE_ERROR. If the collection is automatically null, then the PL/SQL raises COLLECTION_IS_NULL. Some of the examples are shown below:DECLARETYPE NumList IS TABLE OF INTEGER;nums NumList := NumList(10,20,30);ints NumList;...BEGIN...nums(1) := TRUNC(high/low);nums(3) := nums(1);nums(2) := ASCII(’B’);/* Assume execution continues despite the raised exception. */nums(’A’) := 40; -- raises VALUE_ERRORints(1) := 15; -- raises COLLECTION_IS_NULLEND;Comparing Whole CollectionsThe Nested tables and varrays can be automatically null; therefore they can be tested for the nullity, as the example below shows:DECLARETYPE Staff IS TABLE OF Employee;members Staff;BEGIN...IF members IS NULL THEN ... -- condition yields TRUE;END;Though, the collections cannot be compared for equality or inequality. For illustration, the IF condition below is illegal as shown:DECLARETYPE Clientele IS TABLE OF Customer;group1 Clientele := Clientele(...);group2 Clientele := Clientele(...);BEGIN...IF group1 = group2 THEN -- causes compilation error...END IF;END;This restriction also applies to implicit the comparisons. For illustration, the collections cannot appear in an ORDER BY, GROUP BY, or DISTINCT list.
Parameter Default Values As the illustration below shows, you can initialize the IN parameters to the default values. In that way, you can pass various numbers of actual par
Operators on Tables and Rows Row Extraction TUPLE FROM r, SQL has row subqueries. These are just like scalar subqueries except that they may specify more than one column.
What Is a Package? The package is a schema object that group logically related PL/SQL items, types, and subprograms. The Packages usually have 2 parts, a specification & a bo
THEO R Y OF PANSPERMIA - Arrhenius (1908) postulated the cosmic panspermia theory that claims that organisms existed throughout the universe, and their spores, etc., could
Project Description: I want somebody who can help me with an idea that I have been working on for a few months now. The person will require extensive knowledge of warcraft 3 PvP
Transaction Control The Oracle is transaction oriented; that is, Oracle uses the transactions to make sure the data integrity. The transaction is a sequence of SQL data manip
Effects of NULL in Aggregate Operator - SQL Let aggop(x) be an invocation of some aggregate operator aggop in SQL, where x is an expression (usually an open expression) to be
Overriding Default Locking By default, the Oracle locks the data structures for you automatically. Though, you can request exact data locks on rows or tables when it is to you
Exception handling In the PL/SQL, a warning or error condition is known as an exception. The Exceptions can be internally defined (by the run-time system) or user defined. The
Example of ADD CONSTRAINT in SQL Example: Alternative formulation for MAX_ENROLMENTS ALTER TABLE IS_ENROLLED_ON ADD CONSTRAINT MAX_ENROLMENTS CHECK ((SELECT COUNT (*)
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