Boilerplate code for a plugin with the purpose of a SQL query.

SQL-Query-WP-Plugin-boilerplate.php

<?php
/*
Plugin Name: Fix Such and Such Problem
Description: This plugin fixes such and such because such and such is broken
Version: 0.1
Author: Awesome Plugin Meister
*/

if(!class_exists('Such_Such_Fixer')){
  class Such_Such_Fixer{
		public function __construct(){

			#Keep this behind the login firewall
			add_action('admin_init', array($this, 'fix_it'), 9999);
		}

		public function fix_it(){
			$trigger = 'fix-such-such';
			$key = 'magic456';

			#Keep this obscure so only you can pull the trigger
			if(!isset($_GET[$trigger]))
				return;

			if($_GET[$trigger] === $key){
				global $wpdb;
				$sql = $wpdb->prepare("
					UPDATE $wpdb->posts
					SET $wpdb->posts.post_content = REPLACE($wpdb->posts.post_content,'[gallery]','')
					WHERE $wpdb->posts.post_type = 'galleries'
				");
				$result = $wpdb->query($sql);
				if($result)
					show_message('Galleries shortcode deleted for all posts.');
				else
					show_message('Somefing happened when I tried to delete all Z gallery shortcodes.');
				exit;
			}


		}

	}
	new Such_Such_Fixer;
}