Visualizing arrays with a basic computing problem

[datastructures]

I have something that has been bugging me for a while now. From the wikipedia entry on arrays

Because the mathematical concept of a matrix can be represented as a two-dimensional grid, two-dimensional arrays are also sometimes called matrices.

This is the wikipedia page https://en.wikipedia.org/wiki/Array_data_structure.

Take a simple mysql table with the following fields

id, product_name, product_description, product_category,date_updated

The table has products in it and i want to query this table and i want to display the product category as the header and then list the products under the header.

This is the representation in the GUI

For instance i have the following categories i.e tvs, tables, utensils

tvs

product 1
product 2
product 3

tables

product 4
product 5
product 6

utensils

product 7
product 8
product 9


My mysql query would look like this

select * from products order by product_category

I am looking for various snippets on how you can achieve the display as i have described above. I am also looking for various ways you can do this and an explanation as well.

Objectives

Since arrays are stored in contiguous blocks of memory Source: arrays i am trying to wrap my head around the idea of arrays being matrices. Code can be in python or php or javascript and the explanation is what i am most interested in.

Thanks.