add more specific types and column asset documentation

docs/en/reference/schema-representation.rst

@@ -61,4 +61,80 @@ All methods that generate SQL queries for you make much effort to
 get the order of generation correct, so that no problems will ever
 occour with missing links of foreign keys.
 
+Schema Assets
+-------------
 
+A schema asset is considered any abstract atomic unit in a database such as schemas,
+tables, indexes, but also sequences, columns and even identifiers.
+The following chapter gives an overview of all available Doctrine 2
+schema assets with short explanations on their context and usage.
+All schema assets reside in the ``Doctrine\DBAL\Schema`` namespace.
+
+.. note::
+
+    This chapter is far from being completely documented.
+
+Column
+~~~~~~
+
+Represents a table column in the database schema.
+A column consists of a name, a type, portable options, commonly supported options and
+vendors specific options.
+
+Portable options
+^^^^^^^^^^^^^^^^
+
+The following options are considered to be fully portable across all database platforms:
+
+-  **notnull** (boolean): Whether the column is nullable or not. Defaults to ``true``.
+-  **default** (integer|string): The default value of the column if no value was specified.
+   Defaults to ``null``.
+-  **autoincrement** (boolean): Whether this column should use an autoincremented value if
+   no value was specified. Only applies to Doctrine's ``smallint``, ``integer``
+   and ``bigint`` types. Defaults to ``false``.
+-  **length** (integer): The maximum length of the column. Only applies to Doctrine's
+   ``string`` and ``binary`` types. Defaults to ``null`` and is evaluated to ``255``
+   in the platform.
+-  **fixed** (boolean): Whether a ``string`` or ``binary`` Doctrine type column has
+   a fixed length. Defaults to ``false``.
+-  **precision** (integer): The precision of a Doctrine ``decimal`` or ``float`` type
+   column that determines the overall maximum number of digits to be stored (including scale).
+   Defaults to ``10``.
+-  **scale** (integer): The exact number of decimal digits to be stored in a Doctrine
+   ``decimal`` or ``float`` type column. Defaults to ``0``.
+-  **customSchemaOptions** (array): Additional options for the column that are
+   supported by all vendors:
+
+   -  **unique** (boolean): Whether to automatically add a unique constraint for the column.
+      Defaults to ``false``.
+
+Common options
+^^^^^^^^^^^^^^
+
+The following options are not completely portable but are supported by most of the
+vendors:
+
+-  **unsigned** (boolean): Whether a ``smallint``, ``integer`` or ``bigint`` Doctrine
+   type column should allow unsigned values only. Supported by MySQL, SQL Anywhere
+   and Drizzle. Defaults to ``false``.
+-  **comment** (integer|string): The column comment. Supported by MySQL, PostgreSQL,
+   Oracle, SQL Server, SQL Anywhere and Drizzle. Defaults to ``null``.
+
+Vendor specific options
+^^^^^^^^^^^^^^^^^^^^^^^
+
+The following options are completely vendor specific and absolutely not portable:
+
+-  **columnDefinition**: The custom column declaration SQL snippet to use instead
+   of the generated SQL by Doctrine. Defaults to ``null``. This can useful to add
+   vendor specific declaration information that is not evaluated by Doctrine
+   (such as the ``ZEROFILL`` attribute on MySQL).
+-  **customSchemaOptions** (array): Additional options for the column that are
+   supported by some vendors but not portable:
+
+   -  **charset** (string): The character set to use for the column. Currently only supported
+      on MySQL and Drizzle.
+   -  **collate** (string): The collation to use for the column. Currently only supported on
+      SQL Server.
+   -  **check** (string): The check constraint clause to add to the column.
+      Defaults to ``null``.