库存系统数据库设计

Question

I am trying to make an inventory system for a company, when user will enter item to an inventory there is no problem as the table is shown below, however how do i know how many item left when some of the item is sold ? for example I purchased 100 bags and Mr Y purchased 20 bags, how will system show 80 bags left ? Any help would be appreceated. Thanks

CREATE TABLE `inventory` (
 `inv_id` int(11) NOT NULL AUTO_INCREMENT,
 `inv_reference_no` varchar(40) NOT NULL,
 `inv_part_no` varchar(100) NOT NULL,
 `inv_category_id` int(11) NOT NULL,
 `inv_product_name` varchar(200) NOT NULL,
 `inv_quantity` int(11) NOT NULL,
 `inv_description` varchar(500) NOT NULL,
 `inv_cost_price` float(12,2) NOT NULL,
 `inv_cost_sub_total` float(14,2) NOT NULL,
 `inv_product_type` enum('cons','serv','stock') NOT NULL,
 `inv_date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
 PRIMARY KEY (`inv_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8

Answer 1

You can add field say "in_stock" in you table which will store the quantity of products left. Or you can decrement your quantity field everytime any item is purchased. Hope it helps

Answer 2

Well, it should seem straightforward as you already have an 'inv_quantity' field that you could update. I'm not sure if you're having trouble with figuring out how to update it.

Here's some partly pseud-code that could help you. It could start out as UPDATE inventory SET inv_quantity = inv_quantity - quantity_purchased WHERE inv_id = purchased_product_id .

Then soon after, you would SELECT inv_quantity FROM inventory WHERE inv_id = purchased_product_id . The variables quantity_purchased and purchased_product_id will have to be supplied from you with however you're sending form data with your application.