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+.. _sql engines:
+
+===========
+SQL Engines
+===========
+
+.. sidebar:: further read
+
+   - `SQLite <https://www.sqlite.org/index.html>`_
+   - `PostgreSQL <https://www.postgresql.org>`_
+   - `MySQL <https://www.mysql.com>`_
+
+.. contents::
+   :depth: 2
+   :local:
+   :backlinks: entry
+
+.. sidebar:: info
+
+   Initial sponsored by `Search and Discovery Fund
+   <https://nlnet.nl/discovery>`_ of `NLnet Foundation <https://nlnet.nl/>`_.
+
+With the *SQL engines* you can bind SQL databases into SearXNG.  The following
+Relational Database Management System (RDBMS) are supported:
+
+- :ref:`engine sqlite`
+- :ref:`engine postgresql`
+- :ref:`engine mysql_server` & :ref:`engine mariadb_server`
+
+All of the engines above are just commented out in the :origin:`settings.yml
+<searx/settings.yml>`, as you have to set the required attributes for the
+engines, e.g. ``database:`` ...
+
+.. code:: yaml
+
+   - name: ...
+     engine: {sqlite|postgresql|mysql_server}
+     database: ...
+     result_template: {template_name}
+     query_str: ...
+
+By default, the engines use the ``key-value`` template for displaying results /
+see :origin:`simple <searx/templates/simple/result_templates/key-value.html>`
+theme.  If you are not satisfied with the original result layout, you can use
+your own template, set ``result_template`` attribute to ``{template_name}`` and
+place the templates at::
+
+  searx/templates/{theme_name}/result_templates/{template_name}
+
+If you do not wish to expose these engines on a public instance, you can still
+add them and limit the access by setting ``tokens`` as described in section
+:ref:`private engines`.
+
+
+Extra Dependencies
+==================
+
+For using :ref:`engine postgresql` or :ref:`engine mysql_server` you need to
+install additional packages in Python's Virtual Environment of your SearXNG
+instance.  To switch into the environment (:ref:`searxng-src`) you can use
+:ref:`searxng.sh`::
+
+  $ sudo utils/searxng.sh instance cmd bash
+  (searxng-pyenv)$ pip install ...
+
+
+Configure the engines
+=====================
+
+The configuration of the new database engines are similar.  You must put a valid
+SQL-SELECT query in ``query_str``.  At the moment you can only bind at most one
+parameter in your query.  By setting the attribute ``limit`` you can define how
+many results you want from the SQL server.  Basically, it is the same as the
+``LIMIT`` keyword in SQL.
+
+Please, do not include ``LIMIT`` or ``OFFSET`` in your SQL query as the engines
+rely on these keywords during paging.  If you want to configure the number of
+returned results use the option ``limit``.
+
+.. _engine sqlite:
+
+SQLite
+------
+
+.. sidebar:: info
+
+   - :origin:`sqlite.py <searx/engines/sqlite.py>`
+
+.. automodule:: searx.engines.sqlite
+  :members:
+
+
+.. _engine postgresql:
+
+PostgreSQL
+----------
+
+.. _psycopg2: https://www.psycopg.org/install
+
+.. sidebar:: info
+
+   - :origin:`postgresql.py <searx/engines/postgresql.py>`
+   - ``pip install`` `psycopg2-binary <psycopg2>`_
+
+.. automodule:: searx.engines.postgresql
+  :members:
+
+.. _engine mysql_server:
+
+MySQL
+-----
+
+.. sidebar:: info
+
+   - :origin:`mysql_server.py <searx/engines/mysql_server.py>`
+   - ``pip install`` :pypi:`mysql-connector-python <mysql-connector-python>`
+
+
+.. automodule:: searx.engines.mysql_server
+  :members:
+
+.. _engine mariadb_server:
+
+MariaDB
+--------
+
+.. sidebar:: info
+
+   - :origin:`mariadb_server.py <searx/engines/mariadb_server.py>`
+   - ``pip install`` :pypi:`mariadb <mariadb>`
+
+
+.. automodule:: searx.engines.mariadb_server
+  :members: