怎么理解數(shù)據(jù)庫集合元素的刪除

這篇文章主要介紹“怎么理解數(shù)據(jù)庫集合元素的刪除”，在日常操作中，相信很多人在怎么理解數(shù)據(jù)庫集合元素的刪除問題上存在疑惑，小編查閱了各式資料，整理出簡(jiǎn)單好用的操作方法，希望對(duì)大家解答”怎么理解數(shù)據(jù)庫集合元素的刪除”的疑惑有所幫助！接下來，請(qǐng)跟著小編一起來學(xué)習(xí)吧！

我創(chuàng)建了一個(gè)嵌套表類型和過程：

CREATE OR REPLACE TYPE plch_numbers_t IS TABLE OF NUMBER;
/
CREATE OR REPLACE PROCEDURE plch_show_numbers (
   title_in     IN VARCHAR2
, numbers_in   IN plch_numbers_t)
IS
BEGIN
   DBMS_OUTPUT.put_line (title_in);
   FOR rec IN (SELECT COLUMN_VALUE FROM TABLE (numbers_in))
   LOOP
      DBMS_OUTPUT.put_line (rec.COLUMN_VALUE);
   END LOOP;
END;
/

下面的選項(xiàng)用來代替下列代碼塊的 /*BODY*/ 注釋:

DECLARE
   l_numbers   plch_numbers_t
       := plch_numbers_t (12, 23, 34, 45, 56
                        , 67, 78, 89, 90, 100);
BEGIN
   /*BODY*/
   plch_show_numbers ('AFTER DELETE', l_numbers);
END;
/

哪些選項(xiàng)使得這個(gè)塊執(zhí)行之后會(huì)顯示如下文本：

AFTER DELETE
23
45
67
89

換而言之，所有偶數(shù)元素都被刪除了。

(A)

FOR indx IN 1 .. l_numbers.COUNT
LOOP
   IF MOD (indx, 2) = 0
   THEN
      l_numbers.delete (indx);
   END IF;
END LOOP;

SQL> DECLARE
  2    l_numbers plch_numbers_t := plch_numbers_t(12,
  3                                               23,
  4                                               34,
  5                                               45,
  6                                               56,
  7                                               67,
  8                                               78,
  9                                               89,
 10                                               90,
 11                                               100);
 12  BEGIN
 13    FOR indx IN 1 .. l_numbers.COUNT LOOP
 14      IF MOD(indx, 2) = 0 THEN
 15        l_numbers.delete(indx);
 16      END IF;
 17    END LOOP;
 18  
 19    plch_show_numbers('AFTER DELETE', l_numbers);
 20  END;
 21  /
AFTER DELETE
12
34
56
78
90
PL/SQL procedure successfully completed
SQL>

(B)

FOR indx IN 1 .. l_numbers.COUNT
LOOP
   IF MOD (l_numbers (indx), 2) = 0
   THEN
      l_numbers.delete (indx);
   END IF;
END LOOP;

SQL> DECLARE
  2    l_numbers plch_numbers_t := plch_numbers_t(12,
  3                                               23,
  4                                               34,
  5                                               45,
  6                                               56,
  7                                               67,
  8                                               78,
  9                                               89,
 10                                               90,
 11                                               100);
 12  BEGIN
 13    FOR indx IN 1 .. l_numbers.COUNT LOOP
 14      IF MOD(l_numbers(indx), 2) = 0 THEN
 15        l_numbers.delete(indx);
 16      END IF;
 17    END LOOP;
 18  
 19    plch_show_numbers('AFTER DELETE', l_numbers);
 20  END;
 21  /
AFTER DELETE
23
45
67
89
PL/SQL procedure successfully completed
SQL>

(C)

DELETE FROM TABLE (l_numbers)
      WHERE MOD (index_value, 2) = 0;

SQL> DECLARE
  2    l_numbers plch_numbers_t := plch_numbers_t(12,
  3                                               23,
  4                                               34,
  5                                               45,
  6                                               56,
  7                                               67,
  8                                               78,
  9                                               89,
 10                                               90,
 11                                               100);
 12  BEGIN
 13    DELETE FROM TABLE(l_numbers) WHERE MOD(index_value, 2) = 0;
 14  
 15    plch_show_numbers('AFTER DELETE', l_numbers);
 16  END;
 17  /
DECLARE
  l_numbers plch_numbers_t := plch_numbers_t(12,
                                             23,
                                             34,
                                             45,
                                             56,
                                             67,
                                             78,
                                             89,
                                             90,
                                             100);
BEGIN
  DELETE FROM TABLE(l_numbers) WHERE MOD(index_value, 2) = 0;
  plch_show_numbers('AFTER DELETE', l_numbers);
END;
ORA-06550: 第 13 行, 第 15 列: 
PL/SQL: ORA-00903: 表名無效
ORA-06550: 第 13 行, 第 3 列: 
PL/SQL: SQL Statement ignored
SQL>

(D)

FOR rec IN (SELECT *
              FROM TABLE (l_numbers)
             WHERE MOD (COLUMN_VALUE, 2) = 0)
LOOP
   l_numbers.delete (rec.COLUMN_VALUE);
END LOOP;

SQL> DECLARE
  2    l_numbers plch_numbers_t := plch_numbers_t(12,
  3                                               23,
  4                                               34,
  5                                               45,
  6                                               56,
  7                                               67,
  8                                               78,
  9                                               89,
 10                                               90,
 11                                               100);
 12  BEGIN
 13    FOR rec IN (SELECT * FROM TABLE(l_numbers) WHERE MOD(COLUMN_VALUE, 2) = 0) LOOP
 14      l_numbers.delete(rec.COLUMN_VALUE);
 15    END LOOP;
 16  
 17    plch_show_numbers('AFTER DELETE', l_numbers);
 18  END;
 19  /
AFTER DELETE
12
23
34
45
56
67
78
89
90
100
PL/SQL procedure successfully completed
SQL>

實(shí)測(cè)答案為B

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