如何在 PL/SQL 中按表集合使用索引

Posted 2023-03-27

【中文标题】如何在 PL/SQL 中按表集合使用索引

【英文标题】：How to use index by table collections in PL/SQL

【发布时间】：2020-10-29 06:35:20

【问题描述】：

我是 PL/SQL 的新用户，最近在 Stack Overflow 中创建了一个帐户。我正在尝试使用一个循环来检索数据并将其存储在表索引中，然后使用另一个循环来按表显示索引中的数据，但它一直给我一个错误，即找不到数据。这是我的代码：

    SET SERVEROUTPUT ON
    DECLARE
      TYPE dept_table_type IS TABLE OF departments.department_name%TYPE INDEX BY PLS_INTEGER;
      my_dept_table dept_table_type;
      loop_count NUMBER := 10;
      deptno NUMBER := 10;
    BEGIN
      dbms_output.put_line('DEPARTMENT_ID                  DEPARTMENT_NAME');
      LOOP
        SELECT department_name INTO my_dept_table(loop_count)
        FROM departments
        WHERE department_id = deptno;

        deptno := deptno + 10;
        loop_count := loop_count + 10;

        EXIT WHEN loop_count > 100;
      END LOOP;

      FOR I in my_dept_table.FIRST..my_dept_table.LAST
      LOOP
        DBMS_OUTPUT.PUT_LINE(I||'                                   '||my_dept_table(I));
      END LOOP;
    END;
    /


    Result: Error report -
    ORA-01403: no data found
    ORA-06512: at line 18
    01403. 00000 -  "no data found"
    *Cause:    No data was found from the objects.
    *Action:   There was no data from the objects which may be due to end of fetch.

任何人都可以检查代码。我是 PLSQL 的新用户，谢谢。

【参考方案1】：

有两个可疑的地方会导致NO_DATA_FOUND 异常。

第一个是select 语句，如果您尝试获取属于不存在的部门号的部门名称，该语句将失败。

基于 Scott 的 DEPT 表（因为我没有你的表）：这是表的内容：

SQL> select * from dept;

    DEPTNO DNAME                LOC
---------- -------------------- --------------------
        10 ACCOUNTING           NEW YORK
        20 RESEARCH             DALLAS
        30 SALES                CHICAGO
        40 OPERATIONS           BOSTON

你的代码，重写：

SQL> set serveroutput on
SQL>
SQL> DECLARE
  2     TYPE dept_table_type IS TABLE OF dept.dname%TYPE
  3        INDEX BY PLS_INTEGER;
  4
  5     my_dept_table  dept_table_type;
  6     l_deptno       NUMBER := 10;
  7  BEGIN
  8     LOOP
  9        DBMS_OUTPUT.put_line (l_deptno);
 10
 11        SELECT dname                             --> this fails
 12          INTO my_dept_table (l_deptno)
 13          FROM dept
 14         WHERE deptno = l_deptno;
 15
 16        l_deptno := l_deptno + 10;
 17        EXIT WHEN l_deptno > 100;
 18     END LOOP;
 19  END;
 20  /
10
20
30
40
50                            --> because department 50 doesn't exist
DECLARE
*
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 11

那么，该怎么办？处理异常！

SQL> DECLARE
  2     TYPE dept_table_type IS TABLE OF dept.dname%TYPE
  3        INDEX BY PLS_INTEGER;
  4
  5     my_dept_table  dept_table_type;
  6     l_deptno       NUMBER := 10;
  7  BEGIN
  8     LOOP
  9        DBMS_OUTPUT.put_line (l_deptno);
 10
 11        BEGIN
 12           SELECT dname
 13             INTO my_dept_table (l_deptno)
 14             FROM dept
 15            WHERE deptno = l_deptno;
 16        EXCEPTION
 17           WHEN NO_DATA_FOUND
 18           THEN
 19              DBMS_OUTPUT.put_line (l_deptno || ' department does not exist');
 20        END;
 21
 22        l_deptno := l_deptno + 10;
 23        EXIT WHEN l_deptno > 100;
 24     END LOOP;
 25  END;
 26  /
10
20
30
40
50
50 department does not exist
60
60 department does not exist
70
70 department does not exist
80
80 department does not exist
90
90 department does not exist
100
100 department does not exist

PL/SQL procedure successfully completed.

SQL>

---

另一个地方（这是您的代码所遭受的）是当您尝试显示不存在的数组项时。

SQL> DECLARE
  2     TYPE dept_table_type IS TABLE OF dept.dname%TYPE
  3        INDEX BY PLS_INTEGER;
  4
  5     my_dept_table  dept_table_type;
  6     l_deptno       NUMBER := 10;
  7  BEGIN
  8     LOOP
  9        BEGIN
 10           SELECT dname
 11             INTO my_dept_table (l_deptno)
 12             FROM dept
 13            WHERE deptno = l_deptno;
 14        EXCEPTION
 15           WHEN NO_DATA_FOUND
 16           THEN
 17              NULL;
 18        END;
 19
 20        l_deptno := l_deptno + 10;
 21        EXIT WHEN l_deptno > 100;
 22     END LOOP;
 23
 24     DBMS_OUTPUT.put_line ('Number of items: ' || my_dept_table.COUNT);
 25
 26     FOR I IN my_dept_table.FIRST .. my_dept_table.LAST
 27     LOOP
 28        DBMS_OUTPUT.put_line ('i = ' || i);
 29        DBMS_OUTPUT.put_line (my_dept_table (i));
 30     END LOOP;
 31  END;
 32  /
Number of items: 4             --> department numbers 10, 20, 30, 40
i = 10                         --> this is OK - department 10 = ACCOUNTING
ACCOUNTING
i = 11                         --> but, there's no department 11 and you got an error
DECLARE
*
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 29


SQL>

---

建议：完全重写代码以提高效率：

SQL> DECLARE
  2     TYPE dept_table_type IS TABLE OF dept.dname%TYPE
  3        INDEX BY PLS_INTEGER;
  4
  5     my_dept_table  dept_table_type;
  6  BEGIN
  7     SELECT dname
  8       BULK COLLECT INTO my_dept_table
  9       FROM dept;
 10
 11     FOR i IN my_dept_table.FIRST .. my_dept_table.LAST
 12     LOOP
 13        DBMS_OUTPUT.put_line (my_dept_table (i));
 14     END LOOP;
 15  END;
 16  /
ACCOUNTING
RESEARCH
SALES
OPERATIONS

PL/SQL procedure successfully completed.

SQL>