How to store categories with subcategories in the database?

Question

MySQL

List of categories

$list_category = [
        "автоматика",
        "архитектура",
        "бетонные работы",
        "бурение скважин",
        "двери"=>[
            "деревянные"=>[
                "изготовление",
                "установка",
                "реставрация",
            ],
            "металлические"=>[
                "изготовление",
                "установка",
                "реставрация",
            ],
            "пластиковые"=>[
                "изготовление",
                "установка",
                "реставрация",
            ],
        ],
        "земляные работы",
        "камин",
        "кладка"=>[
            "каменная",
            "кирпичная",
        ],
    ];

How to save it in the database (MySQL) to display it like this:

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Category list page

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The first level categories will need to be displayed on this page (ex. Doors, Masonry, etc.)
And the subcategories will be displayed on another page when you click on the first level category (ex. doors => Manufacture, Installation, Restoration)
Another task on the Personal page cabinet :
There is a list of categories:

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The user, in order to submit an ad, selects the categories he needs and the ad will appear in the categories he has chosen.
Now the list of categories in the database is stored in the following form:

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There are no subcategories here.
I display them on the list page like this:

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<?php
    
        
        require_once "../config/function.php";
        $sql = 'SELECT * FROM categories';
        
            $lastChar = null;
            
            foreach ($conndb->query($sql) as $row):
            
                if ($lastChar !== ($currentChar = mb_convert_case(mb_substr($row['category_name'], 0, 1), CASE_UPPER))): 
        
                    $lastChar = $currentChar;
                    
                    
    ?>
                    
                    <h1 class="bukva" id="bukva_<? echo replaceSymbolRuToLat($lastChar); ?>"><? echo mb_convert_case($lastChar, CASE_LOWER); ?></h1>
        
    <?php 
                
                endif;
            
    ?>
                
            <a href="http://localhost/menu_general/masters_page/masters/masters.php">
        
                <div class="kategoriya">
                    <div class="kolichestvo">0</div>
                    <?php echo $row['category_name'] . "\t"; ?>
                </div>
            
            </a>

    <?php

            endforeach;
    
    ?>

Answer 1

Educational program on storing tree-like (hierarchical) data structures in the database
https://gist.github.com/codedokode/10539720