我找到了解决方案：

function rating_install(){
    //Funcion que genera la instalacion del plugin
    global $wpdb;
    $table_name = $wpdb->prefix."rating";
    $create = "CRETA TABLE ".$table_name." ( "
            . "id INT( 11 ) NOT NULL AUTO_INCREMENT PRIMARY KEY, "
            . "url TINYTEXT NOT NULL, "
            . "descripcion TINYTEXT NOT NULL ) ";    
    $wpdb->query($create);
    /*require_once(ABSPATH."wp-admin/includes/upgrade.php");
    dbDelta($create);*/
}

function rating_uninstall(){
    //Funcion que genera la desinstalacion del plugin
    global $wpdb;
    $table_name = $wpdb->prefix."rating";
    $drop = "DROP TABLE IF EXISTS ".$table_name;
    $wpdb->query($drop);
    /*require_once(ABSPATH."wp-admin/includes/upgrade.php");
    dbDelta($drop);*/
}

我写错了create语句，使用$wpdb->查询（$create）很有效！

谢谢大家！

$create = "CRETA TABLE ".$table_name." ( "

可能应阅读：

$create = "CREATE TABLE ".$table_name." ( "

您确实应该使用dbDelta（）函数，因为WordPress将有助于将来的表升级/编辑。否则，您将不得不手动处理数据库升级。不好玩。

您的最终代码将如下所示：

register_activation_hook(__FILE__, \'rating_install\');

function rating_install(){
//Funcion que genera la instalacion del plugin
global $wpdb;
require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
$table_name = $wpdb->prefix .\'rating\';    
$create = 
      "CREATE TABLE ".$table_name." (
      `id` INT NOT NULL AUTO_INCREMENT,
      `url` TINYTEXT NOT NULL,
      `descripcion` TINYTEXT NOT NULL,
      PRIMARY KEY (`id`));";
dbDelta($create);
}

此外，当你卸载插件时，你真的应该把所有这些都放到卸载中。php文件保存在插件目录中。这是卸载插件的正确方法：http://codex.wordpress.org/Function_Reference/register_uninstall_hook

<?php
// uninstall.php

//if uninstall not called from WordPress exit
if ( !defined( \'WP_UNINSTALL_PLUGIN\' ) ) 
    exit();

$option_name = \'any added option name\';
delete_option( $option_name );

// For site options in multisite
delete_site_option( $option_name );

//drop a custom db table
global $wpdb;
$wpdb->query( "DROP TABLE IF EXISTS {$wpbd->prefix}rating" );