How to include attributes of the MySQL table to hook_schema() schema in drupal 7? I am creating a table using hook_schema()

I am referring phpMyadmin to create a new table. In the phpMyadmin there is a
column 'Attributes' 

which has values as 'unsigned' or  on update CURRENT_TIMESTAMP'
I have a row in a table which is of type 'timestamp' and has attributes 'on 
update CURRENT_TIMESTAMP'.
How can I  include this attribute on update CURRENT_TIMESTAMP in the hook_schema() ?

Also there is  a default column in phpMyAdmin how can I add that in hook_schema() ?

the first time I created a hook_module_name.install a table was created as it was specified in the hook_schema()

Then I uninstalled that module but the table was not deleted ?
Now I even removed the .install file cleared the cache , even after this  a table is not created. What can be the solution to this problem.

What I have checked is that it is entering into hook_schema function but the table is not generated at the database. Any hints on this would be appreciated.
You can't use an ON UPDATE unfortunately - Drupal's schema API doesn't give you that sort of dbms-specific control.

You can use unsigned for unsigned and default for a default value though:

$schema['some_table'] = array(
  'fields' =&gt; array(
    'some_field' =&gt; array(
      'type' =&gt; 'int',
      'not null' =&gt; TRUE,
      'unsigned' =&gt; TRUE,
      'default' =&gt; 0,
    ),
  ),
);


See the Schema API docs for the full list of data types and usage.