The keys do not have to be consecutive. An initialization clause is not allowed. There is no constructor notation for associative arrays.
Associative arrays can store data using a primary key value as the index, where the key values are not sequential. Example creates a single element in an associative array, with a subscript of rather than 1. After defining a collection type, you declare variables of that type. You can declare collections as the formal parameters of functions and procedures. That way, you can pass collections to stored subprograms and from one subprogram to another. Example declares a nested table as a parameter of a packaged procedure. To call personnel. See Example and Example See "Defining and Declaring Records".
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Until you initialize it, a nested table or varray is atomically null; the collection itself is null, not its elements. To initialize a nested table or varray, you use a constructor, a system-defined function with the same name as the collection type. This function constructs collections from the elements passed to it. You must explicitly call a constructor for each varray and nested table variable. Associative arrays, the third kind of collection, do not use constructors.
Constructor calls are allowed wherever function calls are allowed. Example initializes a nested table using a constructor, which looks like a function with the same name as the collection type:. Because a nested table does not have a declared size, you can put as many elements in the constructor as necessary. Example initializes a varray using a constructor, which looks like a function with the same name as the collection type:.
You can initialize a collection in its declaration, which is a good programming practice, as shown in Example If you call a constructor without arguments, you get an empty but non-null collection as shown in Example Every reference to an element includes a collection name and a subscript enclosed in parentheses. The subscript determines which element is processed. To reference an element, you specify its subscript using the syntax. The allowed subscript ranges are:.
For varrays, For associative arrays with a string key, the length of the key and number of possible values depends on the VARCHAR2 length limit in the type declaration, and the database character set. Example shows how you can reference the elements of an associative array in a function call. You can assign the value of an expression to a specific element in a collection using the syntax:.
Usually, the subscript must be an integer. Example shows that collections must have the same datatype for an assignment to work.
Having the same element type is not enough. If you assign an atomically null nested table or varray to a second nested table or varray, the second collection must be reinitialized, as shown in Example In the same way, assigning the value NULL to a collection makes it atomically null.
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Example shows some of the ANSI-standard operators that you can apply to nested tables. You can check whether a collection is null. Comparisons such as greater than, less than, and so on are not allowed. This restriction also applies to implicit comparisons. If you want to do such comparison operations, you must define your own notion of what it means for collections to be greater than, less than, and so on, and write one or more functions to examine the collections and their elements and return a true or false value.
For nested tables, you can check whether two nested table of the same declared type are equal or not equal, as shown in Example Because nested tables and varrays can be atomically null, they can be tested for nullity, as shown in Example Example shows that nested tables can be compared for equality or inequality. They cannot be ordered, because there is no greater than or less than comparison. You can test certain properties of a nested table, or compare two nested tables, using ANSI-standard set operations, as shown in Example In addition to collections of scalar or object types, you can also create collections whose elements are collections.
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For example, you can create a nested table of varrays, a varray of varrays, a varray of nested tables, and so on. Example , Example , and Example are some examples showing the syntax and possibilities for multilevel collections. Collection methods make collections easier to use, and make your applications easier to maintain. A collection method is a built-in function or procedure that operates on collections and is called using dot notation. The following apply to collection methods:.
COUNT returns the number of elements that a collection currently contains. COUNT is useful because the current size of a collection is not always known.
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For example, you can fetch a column of Oracle data into a nested table, where the number of elements depends on the size of the result set. By default, the order is based on the binary values of the characters in the string. But if you delete elements from the beginning of a nested table, FIRST returns a number larger than 1. PRIOR n returns the index number that precedes index n in a collection. NEXT n returns the index number that succeeds index n.
These methods are more reliable than looping through a fixed set of subscript values, because elements might be inserted or deleted from the collection during the loop. This is especially true for associative arrays, where the subscripts might not be in consecutive order and so the sequence of subscripts might be 1,2,4,8,16 or 'A','E','I','O','U'.
Example uses NEXT to traverse a nested table from which some elements have been deleted. All deleted elements, regardless of position, are treated alike. This procedure has two forms:. For example, this statement removes the last three elements from nested table courses :. TRIM operates on the internal size of a collection. If TRIM encounters deleted elements, it includes them in its tally.
This procedure has various forms:. If the associative array has a string key, the element corresponding to the key value is deleted. Varrays always have consecutive subscripts, so you cannot delete individual elements except from the end by using the TRIM method. You can store sparse nested tables in the database, just like any other nested tables.
The amount of memory allocated to a nested table can increase or decrease dynamically. As you delete elements, memory is freed page by page. If you delete the entire table, all the memory is freed. Within a subprogram, a collection parameter assumes the properties of the argument bound to it. You can create general-purpose subprograms that take collection parameters and iterate through their elements, add or delete elements, and so on.
For varray parameters, the value of LIMIT is always derived from the parameter type definition, regardless of the parameter mode. The example also includes notes on how to avoid the problems. Execution continues in Example because the raised exceptions are handled in sub-blocks. See "Continuing after an Exception Is Raised". The following list summarizes when a given exception is raised.
In some cases, you can pass invalid subscripts to a method without raising an exception. For example:. Packaged collection types and local collection types are never compatible. For example, suppose you want to call the following packaged procedure:. The second procedure call fails, because the packaged and local VARRAY types are incompatible despite their identical definitions. See "Record Definition". Example and Example illustrate record type declarations. However, records cannot be attributes of object types. Records are easy to process using stored procedures because you can pass just one parameter, instead of a separate parameter for each field.
For example, you might fetch a table row from the EMPLOYEES table into a record, then pass that row as a parameter to a function that computed that employee's vacation allowance or some other abstract value. The function could access all the information about that employee by referring to the fields in the record. The next example shows how to return a record from a function. To make the record type visible across multiple stored functions and stored procedures, declare the record type in a package specification.4840.ru/components/handy/qynu-iphone-6-plus.php
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Like scalar variables, user-defined records can be declared as the formal parameters of procedures and functions:. You can declare and reference nested records. That is, a record can be the component of another record. To set all the fields in a record to default values, assign to it an uninitialized record of the same type, as shown in Example Note that values are assigned separately to each field of a record in Example You cannot assign a list of values to a record using an assignment statement.
There is no constructor-like notation for records. You can assign values to all fields at once only if you assign a record to another record with the same datatype. Having fields that match exactly is not enough, as shown in Example The columns in the select-list must appear in the same order as the fields in your record. Records cannot be tested for nullity, or compared for equality, or inequality. If you want to make such comparisons, write your own function that accepts two records as parameters and does the appropriate checks or comparisons on the corresponding fields.
That makes your code more readable and maintainable. The number of fields in the record must equal the number of columns listed in the INTO clause, and corresponding fields and columns must have compatible datatypes. You can insert this variable without specifying a column list.