Approach using hook_schema (as on Drupal 7)

hook_schema.php

$schema['votingapi_vote'] = array(
    'fields' => array(
      'vote_id' => array('type' => 'serial', 'unsigned' => TRUE, 'not null' => TRUE),
      'entity_type' => array('type' => 'varchar', 'length' => 64, 'not null' => TRUE, 'default' => 'node'),
      'entity_id' => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0),
      'value' => array('type' => 'float', 'not null' => TRUE, 'default' => 0),
      'value_type' => array('type' => 'varchar', 'length' => 64, 'not null' => TRUE, 'default' => 'percent'),
      'tag' => array('type' => 'varchar', 'length' => 64, 'not null' => TRUE, 'default' => 'vote'),
      'uid' => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0),
      'timestamp' => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0),
      'vote_source' => array('type' => 'varchar', 'length' => 255),
    ),
    'primary key' => array('vote_id'),
    'indexes' => array(
      'content_uid' => array('entity_type', 'entity_id', 'uid'),
      'content_uid_2' => array('entity_type', 'uid'),
      'content_source' => array('entity_type', 'entity_id', 'vote_source'),
      'content_value_tag' => array('entity_type', 'entity_id', 'value_type', 'tag'),
    ),
  );