Apparent different sizes when attempting to export a particular mysql database

Question

In a quite old-versioned CentOS-Bash "shared server" environment, I ran the following commands:

current_date="$(date +%F-%T)"
db_user_name_and_db_name="db-username_db-name"
war="$HOME/public_html" # Web Application Root

mkdir -p "${war}/mediawiki_general_backups"

My problem is that If I make a quick export (all tables) of the relevant database from PHPMyAdmin GUI, I get a .sql file of 43MBs.
But, if I export the same database by a CLUI command such as the following, I get a .sql file of 23MBs:

mysqldump \
-u "${db_user_name_and_db_name}" \
-p "${db_user_name_and_db_name}" \
> "${war}/mediawiki_general_backups/${db_user_name_and_db_name}-${current_date}.sql"

I don't know how to explain this difference; do you?

Answer 1

Do quick testing; export a table in PhpMyadmin and with the following command in terminal.

mysqldump -u $UserName -p database table > /tmp/table.sql

Then, open both SQL files with a text-editor; difference should be recognized immediately:
I recognized lots of comments which is exported from PHPMyAdmin and the way of INSERTing data. For example:

Exported SQL has the following header:

-- phpMyAdmin SQL Dump
-- version 4.0.10.20
-- https://www.phpmyadmin.net
--
-- Host: localhost
-- Generation Time: Oct 10, 2019 at 03:48 AM
-- Server version: 5.1.73-log
-- PHP Version: 5.3.3

SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";


/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;

Dumped SQL has the following header:

-- MySQL dump 10.13  Distrib 5.1.73, for redhat-linux-gnu (x86_64)
--
-- Host: localhost    Database: testing
-- ------------------------------------------------------
-- Server version   5.1.73-log

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;