The Right Way to Store an Array in MySQL 8

Introduction

When working with relational databases, such as MySQL, storing and retrieving structured data in the form of arrays can present a challenge. Unlike NoSQL databases which often natively support arrays, MySQL treats data in a more traditional and tabular way. This poses the question: how can you effectively store an array in MySQL 8?

In this tutorial, we take a detailed look into various methods for storing arrays in MySQL, with a focus on their implementation in MySQL 8. We will start from basic techniques and progress towards more complex and efficient solutions.

Understanding the Basics

Prior to MySQL 8, the standard approach to storing arrays was through serialization. That is, encoding an array into a string format that can be saved in a text column. Although this technique remains possible in MySQL 8, its usage is not advised due to lack of efficiency and potential security risks associated with serialization.

Here’s an example of array serialization and deserialization using PHP:

$array = ['apple', 'banana', 'cherry'];
$serializedArray = serialize($array);
// You can now store $serializedArray in a MySQL TEXT field

// To retrieve the array
$retrievedArray = unserialize($retrievedSerializedArray);

However, there are better ways to approach this in MySQL 8. Let’s explore further.

Using JSON Data Type

MySQL 8 introduced the JSON data type, offering a direct way to store complex data structures, including arrays. JSON fields are stored in a binary format which makes them both efficient to access and capable of preserving the array structure without the need for manual serialization.

Example of storing an array as JSON:

CREATE TABLE products (
   id INT AUTO_INCREMENT,
   attributes JSON,
   PRIMARY KEY (id)
);

INSERT INTO products (attributes) VALUES
(JSON_ARRAY('Small', 'Red', 'Cotton'));

Fetching and working with JSON array data:

SELECT id, JSON_EXTRACT(attributes, '$[0]') AS first_attribute
FROM products;

Creating a Set

The SET data type in MySQL allows you to store multiple predefined values in a single column. Each value can only be assigned once which makes SET convenient for arrays with unique elements.

CREATE TABLE shirts (
   id INT AUTO_INCREMENT,
   sizes SET('small', 'medium', 'large'),
   PRIMARY KEY (id)
);

INSERT INTO shirts (sizes) VALUES ('small,medium');

An important limitation of the SET data type is that it can only hold up to 64 distinct members. Furthermore, values need to be defined during table creation, reducing flexibility.

Normalizing Data

One of the most robust methods to store arrays in MySQL is through normalization – using a secondary table to store array elements and then associating them with the primary entry via a foreign key.

CREATE TABLE items (
   id INT AUTO_INCREMENT,
   name VARCHAR(100),
   PRIMARY KEY (id)
);

CREATE TABLE item_tags (
   item_id INT,
   tag VARCHAR(50),
   FOREIGN KEY (item_id) REFERENCES items(id)
);

INSERT INTO items (name) VALUES ('T-Shirt');
INSERT INTO item_tags (item_id, tag) VALUES
(LAST_INSERT_ID(), 'Casual'),
(LAST_INSERT_ID(), 'Cotton');

Normalization benefits from relational database principles and ensures data integrity. However, it requires more complex queries to reconstruct the array.

Using Generated Columns

In MySQL 8, you can also create a virtual generated column to store an array. A generated column is a special column that is always computed from other columns in the same row.

CREATE TABLE athletes (
    id INT AUTO_INCREMENT,
    name VARCHAR(100),
    achievements JSON,
    achievements_text VARCHAR(255) AS (JSON_UNQUOTE(JSON_EXTRACT(achievements, '$'))) STORED, 
    PRIMARY KEY (id)
);

INSERT INTO athletes (name, achievements) 
VALUES ('John Doe', JSON_ARRAY('Olympic Gold', 'World Champion'));

This introduces a method to query JSON data as if it were a regular text field, but care must be taken to handle complex JSON structures properly.

Using Full-Text Search Functionality

For an array of text values, leveraging MySQL’s full-text search capabilities on a TEXT column can be a practical solution if your main goal is to perform efficient searches across these ‘arrays’.

CREATE TABLE comments (
   id INT AUTO_INCREMENT,
   comment TEXT,
   PRIMARY KEY (id)
);

INSERT INTO comments (comment) VALUES
('This product is great, amazing quality, loved the vibrant colors');

SELECT * FROM comments WHERE MATCH(comment)
AGAINST('+great +quality +vibrant' IN BOOLEAN MODE);

This method does not store data in a true array form but provides a workaround for certain use cases.

Conclusion

In summary, there are several ways to simulate the behavior of arrays in MySQL 8, each with its own trade-offs. The JSON data type is powerful for storing complex data structures efficiently, while normalization is ideal for data integrity. It is important to carefully consider the nature of your application and the operations you need to perform on the array data to choose the most suitable method.