update.php

<?php

/** @var rex_addon $this */

require __DIR__ . '/install.php';

if (rex_string::versionCompare($this->getVersion(), '2.1', '<=')) {
    $sql = rex_sql::factory();

    $sql->setQuery(sprintf(
        'INSERT INTO `%s` (domain_id, alias_domain, clang_start) 
            SELECT d.id, a.domain, a.clang_start FROM `%s` a INNER JOIN `%2$s` d ON d.domain = a.alias_domain AND d.alias_domain = "" WHERE a.alias_domain != ""',
        rex::getTable('yrewrite_alias'),
        rex::getTable('yrewrite_domain')
    ));

    $sql->setQuery(sprintf(
        'DELETE FROM `%s` WHERE alias_domain != ""',
        rex::getTable('yrewrite_domain')
    ));

    $sql->setQuery(sprintf(
        'UPDATE `%s` f SET domain_id = (SELECT id FROM `%s` d WHERE d.domain = f.domain)',
        rex::getTable('yrewrite_forward'),
        rex::getTable('yrewrite_domain')
    ));

    rex_sql_table::get(rex::getTable('yrewrite_domain'))
        ->removeColumn('alias_domain')
        ->alter();

    rex_sql_table::get(rex::getTable('yrewrite_forward'))
        ->removeColumn('domain')
        ->alter();

    rex_delete_cache();
}