we have export the product in magento admin panel and changed the products details and import to products. its working fine. But some category id not inserted to table. We have checked with the excel sheet, there is category field in comma separated. My thought is comma is the problem. How to identify the issues?
Simply use 'dataflow' to import the product category ids.
Otherwise you will have to work with whatever code it is that you use to import your products and get it to manage multiple category ids. If this is a one-off import then strip your product spreadsheet down to sku + category_ids then import with dataflow.