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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.
Entering and Exiting If you enter the executable part of an autonomous routine, the major transaction suspends. When you exit the routine, the major transaction resumes. To ex
Initializing and Referencing Collections Until you initialize a collection, a nested table or varray is automatically null (i.e. the collection itself is null, not its elements)
Overloading The PL/SQL overloads the subprogram names. That is, you can use similar name for few different subprograms as long as their formal parameters differ in the number
Implicit Rollbacks Before execute the INSERT, UPDATE, or DELETE statement, the Oracle marks an implicit savepoint . When the statement fails, the Oracle rolls back to the save
SELECT a.child_fname,a.child_lname,concat(b.parent_title,b.parent_fname), b.parent_lname,b.parent_tphone FROM child a,parent b WHERE a.parent_id=b.parent_id ORDER BY a.child_fnam
Sequential Control Dissimilar to the IF and LOOP statements, the GOTO and NULL statements are not important to the PL/SQL programming. The configuration of PL/SQL is such that th
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
Example of COALESCE operator Example: Give the total of marks for each exam (simplified solution) SELECT CourseId, COALESCE ((SELECT SUM (Mark) FROM EXAM_MARK AS EM
Use the MASCOT tables CREDITRS, PORDS and PAYMENTS to write SQL queries to solve the following business problems. These tables / data are available to you via the USQ Oracle server
Using Subqueries A subquery is a query (typically enclosed by parentheses) that appears within another SQL data manipulation statement. If evaluated, the subquery gives a va
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