What data type is "Date" in Postgres?
Why do you need access to the database for this information?

Have you looked here?
http://drupalcode.org/project/date.git/blob/b7502f3a86628e5c4995c01f20ac64d5cee5888b:/date.install

/**
 * @file
 * Install, update and uninstall functions for the Date module.
 */

/**
 * Implements hook_field_schema().
 */
function date_field_schema($field) {
  $db_columns = array();
  switch ($field['type']) {
    case 'datestamp':
      $db_columns['value'] = array(
        'type' =&gt; 'int',
        'not null' =&gt; FALSE,
        'sortable' =&gt; TRUE,
        'views' =&gt; TRUE,
      );
      break;
    case 'datetime':
      $db_columns['value'] = array(
        'type' =&gt; 'datetime',
        'mysql_type' =&gt; 'datetime',
        'pgsql_type' =&gt; 'timestamp without time zone',
        'sqlite_type' =&gt; 'varchar',
        'sqlsrv_type' =&gt; 'smalldatetime',
        'not null' =&gt; FALSE,
        'sortable' =&gt; TRUE,
        'views' =&gt; TRUE,
      );
      break;
    default:
      $db_columns['value'] = array(
        'type' =&gt; 'varchar',
        'length' =&gt; 20,
        'not null' =&gt; FALSE,
        'sortable' =&gt; TRUE,
        'views' =&gt; TRUE,
      );
      break;
  }
  // ... more stuff


The answer to your question is that depending on the Drupal "Date" value you're storing it -- for Postgres it is 1 of the following values:


(drupal field of) datestamp = int DBMS field
(drupal field of)datetime = timestamp without time zone DBMS field
(other drupal field of) date = varchar DBMS field analyzed by Date module on save and usage


EDIT

My answer is for Drupal 7. The same module API can be referenced for Drupal version 6 if needed. You didnt specify what version of Drupal you are using and "CCK" can be apart of both.