Upload Bulk records in Zoho CRM

Upload Bulk records in Zoho CRM

Hi,
 I am trying to upload bulk sales orders into Zoho. The process is so slow via API, so I have decided to change the approach and now I want to upload the Sales orders using csv. Still, I am not sure how I can add the order line products via CSV in the sales orders , along that I am facing issue of duplicate records via API upload, Is there any way to stop that , sales order with same subject not get uploaded multiple times?