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多维 Collection

虽然 collection 只有一维的，但可以模型一个多维的。创建一个 collection，其每个元素也是 collection 。例如，创建一个 varray 的 nested table，一个 varray 的 varray，一个 nested table 的 varray 等。

示例1：演示多维 varray

DECLARE

TYPE t1 IS VARRAY(10) OF INTEGER;

TYPE nt1 IS VARRAY(10) OF t1; -- multilevel varray type

va t1 := t1(2,3,5);

-- initialize multilevel varray

nva nt1 := nt1(va, t1(55,6,73), t1(2,4), va);

i INTEGER;

va1 t1;

BEGIN

-- multilevel access

i := nva(2)(3); -- i will get value 73

DBMS_OUTPUT.PUT_LINE('I = ' || i);

-- add a new varray element to nva

nva.EXTEND;

-- replace inner varray elements

nva(5) := t1(56, 32);

nva(4) := t1(45,43,67,43345);

-- replace an inner integer element

nva(4)(4) := 1; -- replaces 43345 with 1

-- add a new element to the 4th varray element

-- and store integer 89 into it.

nva(4).EXTEND;

nva(4)(5) := 89;

END;

/

示例2：演示多维 nested table

DECLARE

TYPE tb1 IS TABLE OF VARCHAR2(20);

TYPE Ntb1 IS TABLE OF tb1; -- table of table elements

TYPE Tv1 IS VARRAY(10) OF INTEGER;

TYPE ntb2 IS TABLE OF tv1; -- table of varray elements

vtb1 tb1 := tb1('one', 'three');

vntb1 ntb1 := ntb1(vtb1);

vntb2 ntb2 := ntb2(tv1(3,5), tv1(5,7,3));

-- table of varray elements

BEGIN

vntb1.EXTEND;

vntb1(2) := vntb1(1);

-- delete the first element in vntb1

vntb1.DELETE(1);

-- delete the first string

-- from the second table in the nested table

vntb1(2).DELETE(1);

END;

/

示例3：演示多维 associative array

DECLARE

TYPE tb1 IS TABLE OF INTEGER INDEX BY PLS_INTEGER;

-- the following is index-by table of index-by tables

TYPE ntb1 IS TABLE OF tb1 INDEX BY PLS_INTEGER;

TYPE va1 IS VARRAY(10) OF VARCHAR2(20);

-- the following is index-by table of varray elements

TYPE ntb2 IS TABLE OF va1 INDEX BY PLS_INTEGER;

v1 va1 := va1('hello', 'world');

v2 ntb1;

v3 ntb2;

v4 tb1;

v5 tb1; -- empty table

BEGIN

v4(1) := 34;

v4(2) := 46456;

v4(456) := 343;

v2(23) := v4;

v3(34) := va1(33, 456, 656, 343);

-- assign an empty table to v2(35) and try again

v2(35) := v5;

v2(35)(2) := 78; -- it works now

END;

/

 

Collection 异常

示例 4：演示 Collection 异常

演示各种 PL/SQL 预定义的 collection  异常，备注的部分说明如何避免这些异常。

DECLARE

TYPE WordList IS TABLE OF VARCHAR2(5);

words WordList;

err_msg VARCHAR2(100);

PROCEDURE display_error IS

BEGIN

err_msg := SUBSTR(SQLERRM, 1, 100);

DBMS_OUTPUT.PUT_LINE('Error message = ' || err_msg);

END;

BEGIN

BEGIN

words(1) := 10; -- Raises COLLECTION_IS_NULL

--  A constructor has not been used yet.

--  Note: This exception applies to varrays and nested tables,

--  but not to associative arrays which do not need a constructor.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

--  After using a constructor, you can assign values to the elements.

words := WordList('1st', '2nd', '3rd'); -- 3 elements created

--  Any expression that returns a VARCHAR2(5) is valid.

words(3) := words(1) || '+2';

BEGIN

words(3) := 'longer than 5 characters'; -- Raises VALUE_ERROR

--  The assigned value is too long.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words('B') := 'dunno'; -- Raises VALUE_ERROR

--  The subscript (B) of a nested table must be an integer.

--  Note: Also, NULL is not allowed as a subscript.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words(0) := 'zero'; -- Raises SUBSCRIPT_OUTSIDE_LIMIT

--  Subscript 0 is outside the allowed subscript range.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words(4) := 'maybe'; -- Raises SUBSCRIPT_BEYOND_COUNT

--  The subscript (4) exceeds the number of elements in the table.

--  To add new elements, invoke the EXTEND method first.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words.DELETE(1);

IF words(1) = 'First' THEN NULL; END IF;

-- Raises NO_DATA_FOUND

--  The element with subcript (1) was deleted.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

END;

/

在子块处理产生的异常，执行就会继续。下面是一些异常：

Collection 异常	当……产生……
COLLECTION_IS_NULL	尝试操作一个自动为 null 的 collection
NO_DATA_FOUND	一个标值指定了一个被删除的元素，或一个 associative array 不存在的元素
SUBSCRIPT_BEYOND_COUNT	一个标值超过了一个 collection 元素的数量
SUBSCRIPT_OUTSIDE_LIMIT	一个标值超出了被允许的范围
VALUE_ERROR	一个标值为 null 或不能转换成键的类型。若键被定义为 PLS_INTEGER，或标值超出范围，则会产生该异常

在多数情况下，你可以传递一个不可靠的标值给方法，而不会产生异常。例如，当你传递一个 null 给 DELETE(n) 时，该方法什么都不会做。给已经删除的元素赋值，来替换这个已删除的元素，不会产生 NO_DATA_FOUND 异常。

示例 5：演示 DELETE(n) 如何处理不可靠的标值

DECLARE

TYPE NumList IS TABLE OF NUMBER;

nums NumList := NumList(10,20,30);  -- initialize table

BEGIN

nums.DELETE(-1);  -- does not raise SUBSCRIPT_OUTSIDE_LIMIT

nums.DELETE(3);   -- delete 3rd element

DBMS_OUTPUT.PUT_LINE(nums.COUNT);  -- prints 2

nums(3) := 30;    -- allowed; does not raise NO_DATA_FOUND

DBMS_OUTPUT.PUT_LINE(nums.COUNT);  -- prints 3

END;

/

示例 6：演示包和本地 Collection 之间不兼容性

包的 collection 类型与本地 collection 类型不兼容。例如，若你调用包的存储过程，如下所示，第二个存储过程会调用失败，因为，包的和本地的 varray 类型不兼容，尽管它们具有相同的定义。

CREATE PACKAGE pkg AS

TYPE NumList IS TABLE OF NUMBER;

PROCEDURE print_numlist (nums NumList);

END pkg;

/

CREATE PACKAGE BODY pkg AS

PROCEDURE print_numlist (nums NumList) IS

BEGIN

FOR i IN nums.FIRST..nums.LAST LOOP

DBMS_OUTPUT.PUT_LINE(nums(i));

END LOOP;

END;

END pkg;

/

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n1 pkg.NumList := pkg.NumList(2,4); -- type from the package.

n2 NumList := NumList(6,8);         -- local type.

BEGIN

pkg.print_numlist(n1); -- type from pkg is legal

-- The packaged procedure cannot accept

-- a value of the local type (n2)

-- pkg.print_numlist(n2);  -- Causes a compilation error.

END;

/