在执行"count"关键字之前，应在服务器上的存储过程中进行查询.如果只想计数，请注意不要获取查询中的所有列/属性.

Until the implementation of the "count" keyword, you should do your query in a store procedure on the server. Take care to not get all columns/properties in your query if you want only a count.

仅选择ID，例如；

  dc.CreateDocumentQuery(update.SelfLink, "SELECT c.id FROM c")