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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.
%ROWCOUNT When its cursor or cursor variable is opened, the %ROWCOUNT is zeroed. Before the first fetch, the %ROWCOUNT yields 0. Afterward, it yields the number of rows fetche
Procedures The procedure is a subprogram which performs a specific action. You write procedures using the syntax as shown below: PROCEDURE name [(parameter[, parameter, .
Row Operators The Row operators return or reference the particular rows. ALL retains the duplicate rows in the result of a query or in an aggregate expression. The DISTINCT el
Advantages of Exceptions Using the exceptions for the error handling has many benefits. Without an exception handling, every time you issue a command, you should ensure for th
Declaring and Initializing Objects: An object type is once defined and installed in the schema; you can use it to declare the objects in any PL/SQL, subprogram, block or packa
Parameter and Keyword Description: cursor_variable_name: This identifies a cursor variable or the parameter formerly declared within the present scope. host_cursor_va
%TYPE: This attribute gives the datatype of a formerly declared collection, cursor variable, object, field, record, database column, or variable. Datatype: This is simply
Fetching with a Cursor The FETCH statements retrieve the rows in the result set one at a time. After each and every fetch, the cursor advance to the next row in the result set
Using the student and faculty tables create a select query that outputs all students for a specific advisor. Generate the execution plan, select out the explain plan . Create an
Rephrase Conditional Control Statements When computing a logical expression, the PL/SQL uses short-circuit evaluation. That is, the PL/SQL stops evaluating the expression as s
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