Просто взгляните на его схему базы данных в webform.install.
...
$schema['webform_submitted_data'] = array(
'description' => 'Stores all submitted field data for webform submissions.',
'fields' => array(
'nid' => array(
'description' => 'The node identifier of a webform.',
'type' => 'int',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
),
'sid' => array(
'description' => 'The unique identifier for this submission.',
'type' => 'int',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
),
'cid' => array(
'description' => 'The identifier for this component within this node, starts at 0 for each node.',
'type' => 'int',
'size' => 'small',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
),
'no' => array(
'description' => 'Usually this value is 0, but if a field has multiple values (such as a time or date), it may require multiple rows in the database.',
'type' => 'varchar',
'length' => 128,
'not null' => TRUE,
'default' => '0',
),
'data' => array(
'description' => 'The submitted value of this field, may be serialized for some components.',
'type' => 'text',
'size' => 'medium',
'not null' => TRUE,
),
),
'indexes' => array(
'nid' => array('nid'),
'sid_nid' => array('sid', 'nid'),
),
'primary key' => array('nid', 'sid', 'cid', 'no'),
);
...