Gsyfuy

After reading change log for Magento2.3, I come to know now onward in Magento we can add custom table via xml.

so there would be no PHP way to create a table.

So can any one tell me how can I add a custom table in via my custom module.

You can do that by XML.
Check here.

<?xml version="1.0"?>

<!--

/**

 * Copyright © Magento, Inc. All rights reserved.

 * See COPYING.txt for license details.

 */

-->

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

        xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">

    <table name="cms_block" resource="default" engine="innodb" comment="CMS Block Table">

        <column xsi:type="smallint" name="block_id" padding="6" unsigned="false" nullable="false" identity="true"

                comment="Entity Id"/>

        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Block Title"/>

        <column xsi:type="varchar" name="identifier" nullable="false" length="255" comment="Block String Identifier"/>

        <column xsi:type="mediumtext" name="content" nullable="true" comment="Block Content"/>

        <column xsi:type="timestamp" name="creation_time" on_update="false" nullable="false" default="CURRENT_TIMESTAMP"

                comment="Block Creation Time"/>

        <column xsi:type="timestamp" name="update_time" on_update="true" nullable="false" default="CURRENT_TIMESTAMP"

                comment="Block Modification Time"/>

        <column xsi:type="smallint" name="is_active" padding="6" unsigned="false" nullable="false" identity="false"

                default="1" comment="Is Block Active"/>

        <constraint xsi:type="primary" name="PRIMARY">

            <column name="block_id"/>

        </constraint>

        <index name="CMS_BLOCK_TITLE_IDENTIFIER_CONTENT" indexType="fulltext">

            <column name="title"/>

            <column name="identifier"/>

            <column name="content"/>

        </index>

    </table>

    <table name="cms_block_store" resource="default" engine="innodb" comment="CMS Block To Store Linkage Table">

        <column xsi:type="smallint" name="block_id" padding="6" unsigned="false" nullable="false" identity="false"/>

        <column xsi:type="smallint" name="store_id" padding="5" unsigned="true" nullable="false" identity="false"

                comment="Store ID"/>

        <constraint xsi:type="primary" name="PRIMARY">

            <column name="block_id"/>

            <column name="store_id"/>

        </constraint>

        <constraint xsi:type="foreign" name="CMS_BLOCK_STORE_BLOCK_ID_CMS_BLOCK_BLOCK_ID" table="cms_block_store"

                    column="block_id" referenceTable="cms_block" referenceColumn="block_id" onDelete="CASCADE"/>

        <constraint xsi:type="foreign" name="CMS_BLOCK_STORE_STORE_ID_STORE_STORE_ID" table="cms_block_store"

                    column="store_id" referenceTable="store" referenceColumn="store_id" onDelete="CASCADE"/>

        <index name="CMS_BLOCK_STORE_STORE_ID" indexType="btree">

            <column name="store_id"/>

        </index>

    </table>

    <table name="cms_page" resource="default" engine="innodb" comment="CMS Page Table">

        <column xsi:type="smallint" name="page_id" padding="6" unsigned="false" nullable="false" identity="true"

                comment="Entity Id"/>

        <column xsi:type="varchar" name="title" nullable="true" length="255" comment="Page Title"/>

        <column xsi:type="varchar" name="page_layout" nullable="true" length="255" comment="Page Layout"/>

        <column xsi:type="text" name="meta_keywords" nullable="true" comment="Page Meta Keywords"/>

        <column xsi:type="text" name="meta_description" nullable="true" comment="Page Meta Description"/>

        <column xsi:type="varchar" name="identifier" nullable="true" length="100" comment="Page String Identifier"/>

        <column xsi:type="varchar" name="content_heading" nullable="true" length="255" comment="Page Content Heading"/>

        <column xsi:type="mediumtext" name="content" nullable="true" comment="Page Content"/>

        <column xsi:type="timestamp" name="creation_time" on_update="false" nullable="false" default="CURRENT_TIMESTAMP"

                comment="Page Creation Time"/>

        <column xsi:type="timestamp" name="update_time" on_update="true" nullable="false" default="CURRENT_TIMESTAMP"

                comment="Page Modification Time"/>

        <column xsi:type="smallint" name="is_active" padding="6" unsigned="false" nullable="false" identity="false"

                default="1" comment="Is Page Active"/>

        <column xsi:type="smallint" name="sort_order" padding="6" unsigned="false" nullable="false" identity="false"

                default="0" comment="Page Sort Order"/>

        <column xsi:type="text" name="layout_update_xml" nullable="true" comment="Page Layout Update Content"/>

        <column xsi:type="varchar" name="custom_theme" nullable="true" length="100" comment="Page Custom Theme"/>

        <column xsi:type="varchar" name="custom_root_template" nullable="true" length="255"

                comment="Page Custom Template"/>

        <column xsi:type="text" name="custom_layout_update_xml" nullable="true"

                comment="Page Custom Layout Update Content"/>

        <column xsi:type="date" name="custom_theme_from" comment="Page Custom Theme Active From Date"/>

        <column xsi:type="date" name="custom_theme_to" comment="Page Custom Theme Active To Date"/>

        <column xsi:type="varchar" name="meta_title" nullable="true" length="255" comment="Page Meta Title"/>

        <constraint xsi:type="primary" name="PRIMARY">

            <column name="page_id"/>

        </constraint>

        <index name="CMS_PAGE_IDENTIFIER" indexType="btree">

            <column name="identifier"/>

        </index>

        <index name="CMS_PAGE_TITLE_META_KEYWORDS_META_DESCRIPTION_IDENTIFIER_CONTENT" indexType="fulltext">

            <column name="title"/>

            <column name="meta_keywords"/>

            <column name="meta_description"/>

            <column name="identifier"/>

            <column name="content"/>

        </index>

    </table>

    <table name="cms_page_store" resource="default" engine="innodb" comment="CMS Page To Store Linkage Table">

        <column xsi:type="smallint" name="page_id" padding="6" unsigned="false" nullable="false" identity="false"/>

        <column xsi:type="smallint" name="store_id" padding="5" unsigned="true" nullable="false" identity="false"

                comment="Store ID"/>

        <constraint xsi:type="primary" name="PRIMARY">

            <column name="page_id"/>

            <column name="store_id"/>

        </constraint>

        <constraint xsi:type="foreign" name="CMS_PAGE_STORE_PAGE_ID_CMS_PAGE_PAGE_ID" table="cms_page_store"

                    column="page_id" referenceTable="cms_page" referenceColumn="page_id" onDelete="CASCADE"/>

        <constraint xsi:type="foreign" name="CMS_PAGE_STORE_STORE_ID_STORE_STORE_ID" table="cms_page_store"

                    column="store_id" referenceTable="store" referenceColumn="store_id" onDelete="CASCADE"/>

        <index name="CMS_PAGE_STORE_STORE_ID" indexType="btree">

            <column name="store_id"/>

        </index>

    </table>

</schema>

This is just example from Magento 2 CMS module which you can find from /vendor/magento/module-cms/etc/db_schema.xml file.

In Magento 2.3 you need to define table and table fields in /Vendor/Module/etc/db_schema.xml

1) you need provide table name, resource, engine type, comment, collation, charset, onCreate..etc: here is the basic example: <table name="cms_block" resource="default" engine="innodb" comment="CMS Block Table">

2) you need provide tables fileds type, name,nullable,length,length..etc here is the basic example: <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Block Title"/>

3) You need to provide tables constraint type,name,column,referenceTable,referenceColumn..etc for primary OR foreign key here is the basic example with primary key: <constraint xsi:type="primary" name="PRIMARY"><column name="block_id"/><column name="store_id"/></constraint>

4) As basic last you need to provide index with name, indexType ..etc here is the basic example with index: <index name="CMS_BLOCK_TITLE_IDENTIFIER_CONTENT" indexType="fulltext"><column name="title"/><column name="identifier"/><column name="content"/></index>

You can learn more about table schema here: https://devdocs.magento.com/guides/v2.3/extension-dev-guide/declarative-schema/db-schema.html

You can learn more about data and schema patches here: https://devdocs.magento.com/guides/v2.3/extension-dev-guide/declarative-schema/data-patches.html

An example has been mentioned this reference doc. You also refer the core files of Magento v2.3.0 for learning.

<table name="catalog_product_entity_datetime" resource="default" engine="innodb"

           comment="Catalog Product Datetime Attribute Backend Table">

    <column xsi:type="int" name="value_id" padding="11" unsigned="false" nullable="false" identity="true" comment="Value ID"/>

    <column xsi:type="smallint" name="attribute_id" padding="5" unsigned="true" nullable="false" identity="false" default="0" comment="Attribute ID"/>

    <column xsi:type="smallint" name="store_id" padding="5" unsigned="true" nullable="false" identity="false" default="0" comment="Store ID"/>

    <column xsi:type="int" name="entity_id" padding="10" unsigned="true" nullable="false" identity="false" default="0"/>

    <column xsi:type="datetime" name="value" on_update="false" nullable="true" comment="Value"/>

    <constraint xsi:type="primary" referenceId="PRIMARY">

        <column name="value_id"/>

    </constraint>

    <constraint xsi:type="foreign" referenceId="CAT_PRD_ENTT_DTIME_ATTR_ID_EAV_ATTR_ATTR_ID" table="catalog_product_entity_datetime" column="attribute_id" referenceTable="eav_attribute" referenceColumn="attribute_id" onDelete="CASCADE"/>

    <constraint xsi:type="foreign" referenceId="CAT_PRD_ENTT_DTIME_ENTT_ID_CAT_PRD_ENTT_ENTT_ID" table="catalog_product_entity_datetime" column="entity_id" referenceTable="catalog_product_entity" referenceColumn="entity_id" onDelete="CASCADE"/>

    <constraint xsi:type="foreign" referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_STORE_ID_STORE_STORE_ID" table="catalog_product_entity_datetime" column="store_id" referenceTable="store" referenceColumn="store_id" onDelete="CASCADE"/>

    <constraint xsi:type="unique" referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_ENTITY_ID_ATTRIBUTE_ID_STORE_ID">

        <column name="entity_id"/>

        <column name="attribute_id"/>

        <column name="store_id"/>

    </constraint>

    <index referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_ATTRIBUTE_ID" indexType="btree">

        <column name="attribute_id"/>

    </index>

    <index referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_STORE_ID" indexType="btree">

        <column name="store_id"/>

    </index>

</table>