In this chapter, we will discuss the Collections in PL/SQL. A collection is an ordered group of elements having the same data type. Each element is identified by a unique subscript that represents its position in the collection.

PL/SQL provides three collection types −

• Index-by tables or Associative array
• Nested table
• Variable-size array or Varray

Oracle documentation provides the following characteristics for each type of collections −

We have already discussed varray in the chapter ”PL/SQL arrays”. In this chapter, we will discuss the PL/SQL tables.

Both types of PL/SQL tables, i.e., the index-by tables and the nested tables have the same structure and their rows are accessed using the subscript notation. However, these two types of tables differ in one aspect; the nested tables can be stored in a database column and the index-by tables cannot.

Index-By Table

An index-by table (also called an associative array) is a set of key-value pairs. Each key is unique and is used to locate the corresponding value. The key can be either an integer or a string.

An index-by table is created using the following syntax. Here, we are creating an index-by table named table_name, the keys of which will be of the subscript_type and associated values will be of the element_type

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

table_name type_name;

Example

Following example shows how to create a table to store integer values along with names and later it prints the same list of names.

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;
/

When the above code is executed at the SQL prompt, it produces the following result −

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.

Example

Elements of an index-by table could also be a %ROWTYPE of any database table or %TYPE of any database table field. The following example illustrates the concept. We will use the CUSTOMERS table stored in our database as −

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;
/

When the above code is executed at the SQL prompt, it produces the following result −

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

PL/SQL procedure successfully completed

Nested Tables

A nested table is like a one-dimensional array with an arbitrary number of elements. However, a nested table differs from an array in the following aspects −

• An array has a declared number of elements, but a nested table does not. The size of a nested table can increase dynamically.

• An array is always dense, i.e., it always has consecutive subscripts. A nested array is dense initially, but it can become sparse when elements are deleted from it.

A nested table is created using the following syntax −

TYPE type_name IS TABLE OF element_type [NOT NULL];

table_name type_name;

This declaration is similar to the declaration of an index-by table, but there is no INDEX BY clause.

A nested table can be stored in a database column. It can further be used for simplifying SQL operations where you join a single-column table with a larger table. An associative array cannot be stored in the database.

Example

The following examples illustrate the use of nested table −

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;
/

When the above code is executed at the SQL prompt, it produces the following result −

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.

Example

Elements of a nested table can also be a %ROWTYPE of any database table or %TYPE of any database table field. The following example illustrates the concept. We will use the CUSTOMERS table stored in our database as −

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;
/

When the above code is executed at the SQL prompt, it produces the following result −

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

PL/SQL procedure successfully completed.

Collection Methods

PL/SQL provides the built-in collection methods that make collections easier to use. The following table lists the methods and their purpose −

Collection Exceptions

The following table provides the collection exceptions and when they are raised −