How to get total number of products in virtuemart?

I want to display total numbe开发者_开发知识库r of products sold for each product. There are around 30 products in my virtue mart and I want each one's total sold number.

Table named jos_vm_order_item contains product_id and product_quantity with all other information.

How can I display this?

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SELECT O.product_id,
       SUM(O.product_quantity) as Total_Sold
  FROM jos_vm_order_item O
 GROUP BY O.product_id