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/**

 * Generates a table alias for a field data table.

 *

 * The table alias is unique for each unique combination of field name

 * (represented by $tablename), delta_group and language_group.

 *

 * @param $tablename

 *   The name of the data table for this field.

 * @param $field_key

 *   The numeric key of this field in this query.

 * @param $query

 *   The EntityFieldQuery that is executed.

 *

 * @return

 *   A string containing the generated table alias.

 */

function _field_sql_storage_tablealias($tablename, $field_key, EntityFieldQuery $query) {

  // No conditions present: use a unique alias.

  if (empty($query->fieldConditions[$field_key])) {

    return $tablename . $field_key;

  }

  // Find the delta and language condition values and append them to the alias.

  $condition = $query->fieldConditions[$field_key];

  $alias = $tablename;

  $has_group_conditions = FALSE;

  foreach (array('delta', 'language') as $column) {

    if (isset($condition[$column . '_group'])) {

      $alias .= '_' . $column . '_' . $condition[$column . '_group'];

      $has_group_conditions = TRUE;

    }

  }

  // Return the alias when it has delta/language group conditions.

  if ($has_group_conditions) {

    return $alias;

  }

  // Return a unique alias in other cases.

  return $tablename . $field_key;

}

  $query_tables = NULL;

    $table_alias = _field_sql_storage_tablealias($tablename, $key, $query);

      if (!isset($query_tables[$table_alias])) {

        $select_query->join($tablename, $table_alias, "$table_alias.entity_type = $field_base_table.entity_type AND $table_alias.$id_key = $field_base_table.$id_key");

      }

      // Store a reference to the list of joined tables.

      $query_tables =& $select_query->getTables();