move distinct docs to query_clauses

Author: aminalaee

docs/src/piccolo/query_clauses/distinct.rst

@@ -0,0 +1,15 @@
+.. _distinct:
+
+distinct
+=====
+
+You can use ``distinct`` clauses with the following queries:
+
+* :ref:`Select`
+
+.. code-block:: python
+
+    >>> Band.select(Band.name).distinct().run_sync()
+    [{'title': 'Pythonistas'}]
+
+This is equivalent to ``SELECT DISTINCT name FROM band`` in SQL.

docs/src/piccolo/query_types/select.rst

@@ -43,18 +43,6 @@ By using ``as_alias``, the name of the row can be overriden in the response.
 
 This is equivalent to ``SELECT name AS title FROM band`` in SQL.
 
-Distinct
---------
-
-To get ``DISTINCT`` values of a column add `distinct()` to `select` statement.
-
-.. code-block:: python
-
-    >>> Band.select(Band.name).distinct().run_sync()
-    [{'title': 'Pythonistas'}]
-
-This is equivalent to ``SELECT DISTINCT name FROM band`` in SQL.
-
 Joins
 -----
 
@@ -240,6 +228,11 @@ offset
 
 See  :ref:`offset`.
 
+distinct
+~~~~~
+
+See  :ref:`distinct`.
+
 order_by
 ~~~~~~~~