--- a/sql.rst	Tue Mar 05 11:51:35 2013 +0200
+++ b/sql.rst	Tue Mar 05 13:36:07 2013 +0200
@@ -12,3 +12,15 @@
   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)``.
+
+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.