怎么判断数据库集合的密集性

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我创建了这个工具函数来显示一个布尔型变量的值：

CREATE OR REPLACE PROCEDURE plch_bpl (val IN BOOLEAN)ISBEGIN   DBMS_OUTPUT.put_line (      CASEval WHEN TRUE THEN 'TRUE' WHEN FALSE THEN 'FALSE' ELSE 'NULL' END);END plch_bpl;/

下列的选项中都包含了下面这个函数的实现代码：

CREATE OR REPLACE FUNCTION plch_is_dense (numbers_in IN DBMS_SQL.number_table)   RETURN BOOLEAN

我写了另一个帮助过程来测试这个 plch_is_dense 函数:

CREATE OR REPLACE PROCEDURE plch_test_is_denseIS   l_numbers   DBMS_SQL.number_table;BEGIN   l_numbers (1000) := 1;   l_numbers (3000) := 1;   plch_bpl (plch_is_dense (l_numbers));   l_numbers.delete;   l_numbers (2) := 1;   l_numbers (3) := 1;   plch_bpl (plch_is_dense (l_numbers));END;/

哪些选项创建的plch_is_dense使得plch_test_is_dense在执行之后会显示这两行文本？

FALSETRUE

(A)

ISBEGIN   RETURN numbers_in.COUNT = (numbers_in.LAST - numbers_in.FIRST);END;

(B)

IS   l_number   NUMBER;BEGIN   FOR indx IN numbers_in.FIRST .. numbers_in.LAST   LOOP      l_number := numbers_in (indx);   END LOOP;   RETURN TRUE;EXCEPTION   WHEN NO_DATA_FOUND   THEN      RETURN FALSE;END;

(C)

IS   l_number   NUMBER;BEGIN   FOR indx IN 1 .. numbers_in.COUNT   LOOP      l_number := numbers_in (indx);   END LOOP;   RETURN TRUE;EXCEPTION   WHEN NO_DATA_FOUND   THEN      RETURN FALSE;END;

(D)

ISBEGIN   RETURN numbers_in.COUNT = (numbers_in.LAST - numbers_in.FIRST + 1);END;

运行结果如下

(A)

CREATE OR REPLACE FUNCTION plch_is_dense(numbers_in IN DBMS_SQL.number_table)  RETURN BOOLEAN ISBEGIN  RETURN numbers_in.COUNT =(numbers_in.LAST - numbers_in.FIRST);END;/

SQL> exec plch_test_is_dense;FALSEFALSEPL/SQL procedure successfully completedSQL>

(B)

CREATE OR REPLACE FUNCTION plch_is_dense(numbers_in IN DBMS_SQL.number_table)  RETURN BOOLEAN IS  l_number NUMBER;BEGIN  FOR indx IN numbers_in.FIRST .. numbers_in.LAST LOOP    l_number := numbers_in(indx);  END LOOP;  RETURN TRUE;EXCEPTION  WHEN NO_DATA_FOUND THEN    RETURN FALSE;END;/

SQL> exec plch_test_is_dense;FALSETRUEPL/SQL procedure successfully completedSQL>

(C)

CREATE OR REPLACE FUNCTION plch_is_dense(numbers_in IN DBMS_SQL.number_table)  RETURN BOOLEAN IS  l_number NUMBER;BEGIN  FOR indx IN 1 .. numbers_in.COUNT LOOP    l_number := numbers_in(indx);  END LOOP;  RETURN TRUE;EXCEPTION  WHEN NO_DATA_FOUND THEN    RETURN FALSE;END;/

SQL> exec plch_test_is_dense;FALSEFALSEPL/SQL procedure successfully completedSQL>

(D)

CREATE OR REPLACE FUNCTION plch_is_dense(numbers_in IN DBMS_SQL.number_table)  RETURN BOOLEAN ISBEGIN  RETURN numbers_in.COUNT =(numbers_in.LAST - numbers_in.FIRST + 1);END;/

SQL> exec plch_test_is_dense;FALSETRUEPL/SQL procedure successfully completedSQL>

10-31答案BD. 对于非密集型的COLLECTION访问不能从1开始，而是要用FIRST方法。访问不存在的元素会引发NO_DATA_FOUND异常。

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