InstallSchema.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Magento\Persistent\Setup;

use Magento\Framework\Setup\InstallSchemaInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\SchemaSetupInterface;

/**
 * @codeCoverageIgnore
 */
class InstallSchema implements InstallSchemaInterface
{
    /**
     * @var string
     */
    private static $connectionName = 'checkout';

    /**
     * {@inheritdoc}
     */
    public function install(SchemaSetupInterface $setup, ModuleContextInterface $context)
    {
        $installer = $setup;
        $installer->startSetup();

        /**
         * Create table 'persistent_session'
         */
        $table = $installer->getConnection()->newTable(
            $installer->getTable('persistent_session')
        )->addColumn(
            'persistent_id',
            \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
            null,
            ['identity' => true, 'primary' => true, 'nullable' => false, 'unsigned' => true],
            'Session id'
        )->addColumn(
            'key',
            \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
            50,
            ['nullable' => false],
            'Unique cookie key'
        )->addColumn(
            'customer_id',
            \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
            null,
            ['unsigned' => true],
            'Customer id'
        )->addColumn(
            'website_id',
            \Magento\Framework\DB\Ddl\Table::TYPE_SMALLINT,
            null,
            ['unsigned' => true, 'nullable' => false, 'default' => '0'],
            'Website ID'
        )->addColumn(
            'info',
            \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
            '64k',
            [],
            'Session Data'
        )->addColumn(
            'updated_at',
            \Magento\Framework\DB\Ddl\Table::TYPE_TIMESTAMP,
            null,
            ['nullable' => false, 'default' => \Magento\Framework\DB\Ddl\Table::TIMESTAMP_INIT_UPDATE],
            'Updated At'
        )->addIndex(
            $installer->getIdxName('persistent_session', ['key']),
            ['key'],
            ['type' => \Magento\Framework\DB\Adapter\AdapterInterface::INDEX_TYPE_UNIQUE]
        )->addIndex(
            $installer->getIdxName('persistent_session', ['customer_id']),
            ['customer_id'],
            ['type' => \Magento\Framework\DB\Adapter\AdapterInterface::INDEX_TYPE_UNIQUE]
        )->addIndex(
            $installer->getIdxName('persistent_session', ['updated_at']),
            ['updated_at']
        )->addForeignKey(
            $installer->getFkName('persistent_session', 'customer_id', 'customer_entity', 'entity_id'),
            'customer_id',
            $installer->getTable('customer_entity'),
            'entity_id',
            \Magento\Framework\DB\Ddl\Table::ACTION_CASCADE
        )->addForeignKey(
            $installer->getFkName('persistent_session', 'website_id', 'store_website', 'website_id'),
            'website_id',
            $installer->getTable('store_website'),
            'website_id',
            \Magento\Framework\DB\Ddl\Table::ACTION_CASCADE
        )->setComment(
            'Persistent Session'
        );

        $installer->getConnection()->createTable($table);

        /**
         * Alter quote table with is_persistent flag
         *
         */
        $installer->getConnection(self::$connectionName)->addColumn(
            $installer->getTable('quote', self::$connectionName),
            'is_persistent',
            [
                'type' => \Magento\Framework\DB\Ddl\Table::TYPE_SMALLINT,
                'unsigned' => true,
                'default' => '0',
                'comment' => 'Is Quote Persistent'
            ]
        );

        $installer->endSetup();

    }
}