--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sql.rst	Tue Mar 12 23:38:55 2013 +0200
@@ -0,0 +1,27 @@
+.. -*- coding: utf-8; -*-
+.. include:: HEADER.rst
+
+======
+ SQL.
+======
+.. contents::
+
+Joins.
+======
+
+  http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html
+                A Visual Explanation of SQL Joins.
+
+Primary key length.
+===================
+
+For ``int`` type (32-bit): ``NUMBER(9)``. For ``long`` type (64-bit):
+``NUMBER(18)``.
+
+Oracle allow up to 38 significant digits in ``NUMBER`` and up to 28 digits in
+``SEQUENCE``.
+
+  http://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm
+                Oracle Data Types
+  http://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_6015.htm
+                CREATE SEQUENCE.