Array and Multiset Types in SQL | Database Management System (DBMS) - Software Development PDF Download

Introduction

In the world of databases, SQL (Structured Query Language) is a widely used language for managing and manipulating data. One of the key features of SQL DBMS (Database Management Systems) is its support for various data types, including arrays and multisets. In this article, we will explore these types, understand their usage, and provide examples to help beginners grasp the concept effectively.

Understanding Array Types

An array is a collection of values of the same data type, which can be stored and accessed as a single entity. SQL DBMS provides support for arrays, allowing us to store and query data in a more structured manner.

Syntax for Creating an Array Type

To create an array type, we use the CREATE TYPE statement in SQL. Here's an example:

CREATE TYPE colors_array AS VARRAY(5) OF VARCHAR(20);

In the above code, we create a new array type called colors_array, which can store up to five strings of maximum length 20 characters.

Working with Arrays

Once an array type is created, we can use it as a column type in a table. Here's an example of creating a table that includes an array column:

CREATE TABLE products (

   id INT,

   name VARCHAR(50),

   colors colors_array

);

Now, let's insert some data into the products table:

INSERT INTO products (id, name, colors)

VALUES (1, 'Shirt', colors_array('Red', 'Blue', 'Green'));

To retrieve data from the array column, we can use the array index notation. For example, to get the second color of the first product:

SELECT colors[2] FROM products WHERE id = 1;

The output would be Blue.

Understanding Multiset Types

A multiset, also known as a bag, is a collection of values where duplicate values are allowed. Unlike arrays, multisets don't have a fixed length and can grow dynamically.

Syntax for Creating a Multiset Type

To create a multiset type, we use the CREATE TYPE statement along with the MULTISET keyword. Here's an example:

CREATE TYPE fruits_multiset AS TABLE OF VARCHAR(20);

In the above code, we create a new multiset type called fruits_multiset, which can store an arbitrary number of strings of maximum length 20 characters.

Working with Multisets
Similar to arrays, once a multiset type is created, we can use it as a column type in a table. Here's an example:

CREATE TABLE shopping_cart (

   id INT,

   items fruits_multiset

);

Let's insert some data into the shopping_cart table:

INSERT INTO shopping_cart (id, items)

VALUES (1, fruits_multiset('Apple', 'Banana', 'Apple', 'Orange'));

To retrieve data from the multiset column, we can use the TABLE() function to unnest the elements. For example, to get the distinct items in the shopping cart:

SELECT DISTINCT item

FROM TABLE(shopping_cart.items);

The output would be Apple, Banana, and Orange.

Sample Problems with Solutions

1. Problem: Create a table named employees with a column skills of type skills_array that can store up to 10 skills as strings.

CREATE TYPE skills_array AS VARRAY(10) OF VARCHAR(50);

CREATE TABLE employees (

   id INT,

   name VARCHAR(50),

   skills skills_array

);

2. Problem: Insert data into the employees table, specifying skills for an employee with id = 1.

INSERT INTO employees (id, name, skills)

VALUES (1, 'John Doe', skills_array('SQL', 'Python', 'Java'));

3. Problem: Retrieve the second skill of the employee with id = 1.

SELECT skills[2] FROM employees WHERE id = 1;

Output

Python

Conclusion

Arrays and multisets provide powerful capabilities for storing and querying structured data in SQL DBMS. By using these types, you can organize and manipulate data more efficiently, allowing for more flexible and expressive database designs. With the examples and explanations provided in this article, beginners should now have a good understanding of array and multiset types in SQL DBMS, enabling them to apply this knowledge to their own database projects.