You have not used
@Supplier_Name
in your sql query, could one of the item_name supposed to be supplier_name?
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[round 2]
So the @Supplier_Name has not effect here, why add it as parameter?
You sql query is saying that "Look for those records whose item_name=@item_name, if found update their item_name to @item_name", did you notice something amiss here?
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[round 3]
When you do update, you must have the Where clause to indicate which existing records to update, apparently, it cannot be item_name, because the new value (@item_name) that you give have not existed in the table yet. I think you are trying to change the name of an existing item, right? Does the item has an id? if so, use it in the where clause.