Mryntu

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>