docs: add the user guide

Author: kenjis

user_guide_src/source/changelogs/v4.2.0.rst

@@ -68,7 +68,7 @@ Database
     - It can access Oracle Database and supports SQL and PL/SQL statements.
 - QueryBuilder raw SQL string support
     - Added the class ``CodeIgniter\Database\RawSql`` which expresses raw SQL strings.
-    - :ref:`select() <query-builder-select-rawsql>`, :ref:`where() <query-builder-where-rawsql>`, :ref:`like() <query-builder-like-rawsql>` accept the ``CodeIgniter\Database\RawSql`` instance.
+    - :ref:`select() <query-builder-select-rawsql>`, :ref:`where() <query-builder-where-rawsql>`, :ref:`like() <query-builder-like-rawsql>`, :ref:`join() <query-builder-join-rawsql>` accept the ``CodeIgniter\Database\RawSql`` instance.
 
 Others
 ======

user_guide_src/source/database/query_builder.rst

@@ -234,6 +234,17 @@ outer``, and ``right outer``.
 
 .. literalinclude:: query_builder/020.php
 
+.. _query-builder-join-rawsql:
+
+RawSql
+^^^^^^
+
+Since v4.2.0, ``$builder->join()`` accepts a ``CodeIgniter\Database\RawSql`` instance, which expresses raw SQL strings.
+
+.. literalinclude:: query_builder/102.php
+
+.. warning:: When you use ``RawSql``, you MUST escape the data manually. Failure to do so could result in SQL injections.
+
 *************************
 Looking for Specific Data
 *************************

user_guide_src/source/database/query_builder/102.php

@@ -0,0 +1,7 @@
+<?php
+
+use CodeIgniter\Database\RawSql;
+
+$sql = 'user.id = device.user_id AND ((1=1 OR 1=1) OR (1=1 OR 1=1))';
+$builder->join('user', new RawSql($sql), 'LEFT');
+// Produces: LEFT JOIN "user" ON user.id = device.user_id AND ((1=1 OR 1=1) OR (1=1 OR 1=1))