Wordpress custon database table.

Custom-db-table.php

<?php

function wp_setup_translations_table(){
    global $wpdb;
    $table_name = $wpdb->prefix . "translations";  //get the database table prefix to create my new table

    $sql = "CREATE TABLE $table_name (
      id int(10) unsigned NOT NULL AUTO_INCREMENT,
      identifier varchar(255) NOT NULL,
      translation varchar(255) NOT NULL,
      lang varchar(5) NOT NULL,
      notes varchar(255) DEFAULT NULL,
      PRIMARY KEY  (id),
      KEY Index2 (lang),
      KEY Index3 (identifier)
    ) ENGINE=InnoDB DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;"; // better use: utf8mb4_0900_ai_ci
    
    require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
    dbDelta( $sql );
}

// Create subscribers table
function wp_setup_subscribers_table() {
    global $wpdb;
    $table_name = $wpdb->prefix . 'subscribers';
    
    $sql = "CREATE TABLE $table_name (
      id bigint(21) NOT NULL AUTO_INCREMENT,      
      email varchar (190) NOT NULL,
      PRIMARY KEY  (id)
    ) ENGINE=InnoDB DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;"; // better use: utf8mb4_0900_ai_ci

    require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
    dbDelta( $sql );
}

// In function
add_action('init', 'wp_setup_subscribers_table');

// In theme
add_action('after_switch_theme', 'wp_setup_subscribers_table');

// In plugin
register_activation_hook(__FILE__, 'wp_setup_subscribers_table');

/**
 * Register the REST API wp-learn-form-submissions-api/v1/form-submission routes
 */
add_action( 'rest_api_init', 'wp_learn_register_routes' );
function wp_learn_register_routes() {
    // Register the routes
    // GET https://example.test/wp-json/wp-learn-form-submissions-api/v1/form-submissions
    register_rest_route(
        'wp-learn-form-submissions-api/v1',
        '/form-submissions/',
        array(
            'methods'  => 'GET',
            'callback' => 'wp_learn_get_form_submissions',
            'permission_callback' => '__return_true',
            // 'permission_callback' => 'wp_learn_require_permissions'
        )
    );
  
    // POST https://example.test/wp-json/wp-learn-form-submissions-api/v1/form-submissions
    register_rest_route(
        'wp-learn-form-submissions-api/v1',
        '/form-submission/',
        array(
            'methods'  => 'POST',
            'callback' => 'wp_learn_create_form_submission',
            'permission_callback' => '__return_true',
            // 'permission_callback' => 'wp_learn_require_permissions'
        )
    );
  
    // GET single https://example.test/wp-json/wp-learn-form-submissions-api/v1/form-submission/1
    register_rest_route(
        'wp-learn-form-submissions-api/v1',
        '/form-submission/(?P<id>\d+)',
        array(
            'methods'  => 'GET',
            'callback' => 'wp_learn_rest_get_form_submission',
            'permission_callback' => '__return_true',
            // 'permission_callback' => 'wp_learn_require_permissions'
        )
    );
}

/**
 * GET callback for the wp-learn-form-submissions-api/v1/form-submission route
 *
 * @return array|object|stdClass[]|null
 */
function wp_learn_get_form_submissions() {
    global $wpdb;
    $table_name = $wpdb->prefix . 'form_submissions';
    $results = $wpdb->get_results( "SELECT * FROM $table_name" );
    return $results;
}

// GET https://example.test/wp-json/wp-learn-form-submissions-api/v1/form-submission/1
function wp_learn_rest_get_form_submission( $request ) {
    $id = $request['id'];
    global $wpdb;
    $table_name = $wpdb->prefix . 'form_submissions';
    $results = $wpdb->get_results( "SELECT * FROM $table_name WHERE id = $id" );
    return $results[0];
}

/**
 * POST callback for the wp-learn-form-submissions-api/v1/form-submission route
 *
 * @param $request
 *
 * @return void
 */
function wp_learn_create_form_submission( $request ){
    global $wpdb;
    $table_name = $wpdb->prefix . 'form_submissions';

    $rows = $wpdb->insert(
        $table_name,
        array(
            'name' => $request['name'],
            'email' => $request['email'],
        )
    );

    return $rows;
}

// Check user permissions
function wp_learn_require_permissions() {
    return current_user_can( 'edit_posts' );
}