📌  相关文章
📜  PL / SQL-集合

📅  最后修改于: 2020-11-26 06:01:55             🧑  作者: Mango

在本章中，我们将讨论PL / SQL中的集合。集合是具有相同数据类型的元素的有序组。每个元素由代表其在集合中位置的唯一下标标识。

PL / SQL提供了三种收集类型-

  • 索引表或关联数组
  • 嵌套表
  • 可变大小数组或Varray

Oracle文档为每种类型的集合提供以下特征-

Collection Type Number of Elements Subscript Type Dense or Sparse Where Created Can Be Object Type Attribute
Associative array (or index-by table) Unbounded String or integer Either Only in PL/SQL block No
Nested table Unbounded Integer Starts dense, can become sparse Either in PL/SQL block or at schema level Yes
Variablesize array (Varray) Bounded Integer Always dense Either in PL/SQL block or at schema level Yes

我们已经在“ PL / SQL数组”一章中讨论了varray。在本章中，我们将讨论PL / SQL表。

两种类型的PL / SQL表(即索引表和嵌套表)都具有相同的结构，并且它们的行使用下标符号访问。但是，这两种类型的表在一个方面有所不同。嵌套表可以存储在数据库列中，而索引表则不能。

按表索引

索引表(也称为关联数组)是一组键值对。每个键都是唯一的，用于定位相应的值。键可以是整数或字符串。

使用以下语法创建索引表。在这里，我们正在创建一个名为table_name的索引表，该表的键将为subscript_type，而关联的值将为element_type

TYPE type_name IS TABLE OF element_type [NOT NULL] INDEX BY subscript_type; 
 
table_name type_name;

例

下面的示例演示如何创建一个表来存储整数值和名称，然后再打印出相同的名称列表。

DECLARE 
   TYPE salary IS TABLE OF NUMBER INDEX BY VARCHAR2(20); 
   salary_list salary; 
   name   VARCHAR2(20); 
BEGIN 
   -- adding elements to the table 
   salary_list('Rajnish') := 62000; 
   salary_list('Minakshi') := 75000; 
   salary_list('Martin') := 100000; 
   salary_list('James') := 78000;  
   
   -- printing the table 
   name := salary_list.FIRST; 
   WHILE name IS NOT null LOOP 
      dbms_output.put_line 
      ('Salary of ' || name || ' is ' || TO_CHAR(salary_list(name))); 
      name := salary_list.NEXT(name); 
   END LOOP; 
END; 
/

当以上代码在SQL提示符下执行时，将产生以下结果-

Salary of James is 78000 
Salary of Martin is 100000 
Salary of Minakshi is 75000 
Salary of Rajnish is 62000  

PL/SQL procedure successfully completed.

例

索引表的元素也可以是任何数据库表的％ROWTYPE或任何数据库表字段的％TYPE 。以下示例说明了该概念。我们将使用存储在数据库中的CUSTOMERS表作为-

Select * from customers;  

+----+----------+-----+-----------+----------+ 
| ID | NAME     | AGE | ADDRESS   | SALARY   | 
+----+----------+-----+-----------+----------+ 
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 | 
|  2 | Khilan   |  25 | Delhi     |  1500.00 | 
|  3 | kaushik  |  23 | Kota      |  2000.00 | 
|  4 | Chaitali |  25 | Mumbai    |  6500.00 | 
|  5 | Hardik   |  27 | Bhopal    |  8500.00 | 
|  6 | Komal    |  22 | MP        |  4500.00 | 
+----+----------+-----+-----------+----------+  

DECLARE 
   CURSOR c_customers is 
      select name from customers; 

   TYPE c_list IS TABLE of customers.Name%type INDEX BY binary_integer; 
   name_list c_list; 
   counter integer :=0; 
BEGIN 
   FOR n IN c_customers LOOP 
      counter := counter +1; 
      name_list(counter) := n.name; 
      dbms_output.put_line('Customer('||counter||'):'||name_lis t(counter)); 
   END LOOP; 
END; 
/

当以上代码在SQL提示符下执行时，将产生以下结果-

Customer(1): Ramesh  
Customer(2): Khilan  
Customer(3): kaushik     
Customer(4): Chaitali  
Customer(5): Hardik  
Customer(6): Komal  

PL/SQL procedure successfully completed

嵌套表

嵌套表就像带有任意数量元素的一维数组。但是，嵌套表在以下方面与数组不同：

  • 数组具有声明的元素数，但嵌套表则没有。嵌套表的大小可以动态增加。

  • 数组始终是密集的，即，它总是具有连续的下标。嵌套数组最初是密集的，但是当从其中删除元素时，它可能变得稀疏。

嵌套表使用以下语法创建-

TYPE type_name IS TABLE OF element_type [NOT NULL]; 
 
table_name type_name;

此声明类似于索引表的声明，但是没有INDEX BY子句。

嵌套表可以存储在数据库列中。在将单列表与较大表连接在一起时，它还可用于简化SQL操作。关联数组无法存储在数据库中。

例

以下示例说明了嵌套表的用法-

DECLARE 
   TYPE names_table IS TABLE OF VARCHAR2(10); 
   TYPE grades IS TABLE OF INTEGER;  
   names names_table; 
   marks grades; 
   total integer; 
BEGIN 
   names := names_table('Kavita', 'Pritam', 'Ayan', 'Rishav', 'Aziz'); 
   marks:= grades(98, 97, 78, 87, 92); 
   total := names.count; 
   dbms_output.put_line('Total '|| total || ' Students'); 
   FOR i IN 1 .. total LOOP 
      dbms_output.put_line('Student:'||names(i)||', Marks:' || marks(i)); 
   end loop; 
END; 
/

当以上代码在SQL提示符下执行时，将产生以下结果-

Total 5 Students 
Student:Kavita, Marks:98 
Student:Pritam, Marks:97 
Student:Ayan, Marks:78 
Student:Rishav, Marks:87 
Student:Aziz, Marks:92  

PL/SQL procedure successfully completed.

例

嵌套表的元素也可以是任何数据库表的％ROWTYPE或任何数据库表字段的％TYPE。以下示例说明了该概念。我们将使用存储在数据库中的CUSTOMERS表作为-

Select * from customers;  

+----+----------+-----+-----------+----------+ 
| ID | NAME     | AGE | ADDRESS   | SALARY   | 
+----+----------+-----+-----------+----------+ 
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 | 
|  2 | Khilan   |  25 | Delhi     |  1500.00 | 
|  3 | kaushik  |  23 | Kota      |  2000.00 | 
|  4 | Chaitali |  25 | Mumbai    |  6500.00 | 
|  5 | Hardik   |  27 | Bhopal    |  8500.00 | 
|  6 | Komal    |  22 | MP        |  4500.00 | 
+----+----------+-----+-----------+----------+ 

DECLARE 
   CURSOR c_customers is  
      SELECT  name FROM customers;  
   TYPE c_list IS TABLE of customerS.No.ame%type; 
   name_list c_list := c_list(); 
   counter integer :=0; 
BEGIN 
   FOR n IN c_customers LOOP 
      counter := counter +1; 
      name_list.extend; 
      name_list(counter)  := n.name; 
      dbms_output.put_line('Customer('||counter||'):'||name_list(counter)); 
   END LOOP; 
END; 
/

当以上代码在SQL提示符下执行时，将产生以下结果-

Customer(1): Ramesh  
Customer(2): Khilan  
Customer(3): kaushik     
Customer(4): Chaitali  
Customer(5): Hardik  
Customer(6): Komal  

PL/SQL procedure successfully completed.

收集方法

PL / SQL提供了使收集更易于使用的内置收集方法。下表列出了方法及其用途-

S.No Method Name & Purpose
1

EXISTS(n)

Returns TRUE if the nth element in a collection exists; otherwise returns FALSE.
2

COUNT

Returns the number of elements that a collection currently contains.
3

LIMIT

Checks the maximum size of a collection.
4

FIRST

Returns the first (smallest) index numbers in a collection that uses the integer subscripts.
5

LAST

Returns the last (largest) index numbers in a collection that uses the integer subscripts.
6

PRIOR(n)

Returns the index number that precedes index n in a collection.
7

NEXT(n)

Returns the index number that succeeds index n.
8

EXTEND

Appends one null element to a collection.
9

EXTEND(n)

Appends n null elements to a collection.
10

EXTEND(n,i)

Appends n copies of the ith element to a collection.
11

TRIM

Removes one element from the end of a collection.
12

TRIM(n)

Removes n elements from the end of a collection.
13

DELETE

Removes all elements from a collection, setting COUNT to 0.
14

DELETE(n)

Removes the nth element from an associative array with a numeric key or a nested table. If the associative array has a string key, the element corresponding to the key value is deleted. If n is null, DELETE(n) does nothing.
15

DELETE(m,n)

Removes all elements in the range m..n from an associative array or nested table. If m is larger than n or if m or n is null, DELETE(m,n) does nothing.

集合异常

下表提供了收集异常及其引发时间-

Collection Exception Raised in Situations
COLLECTION_IS_NULL You try to operate on an atomically null collection.
NO_DATA_FOUND A subscript designates an element that was deleted, or a nonexistent element of an associative array.
SUBSCRIPT_BEYOND_COUNT A subscript exceeds the number of elements in a collection.
SUBSCRIPT_OUTSIDE_LIMIT A subscript is outside the allowed range.
VALUE_ERROR A subscript is null or not convertible to the key type. This exception might occur if the key is defined as a PLS_INTEGER range, and the subscript is outside this range.