The title is indeed terrible but I have no idea what to put. I am working on a Bill of Materials app and I’m starting out with the database layout and the REST API to interact with the database.

I currently have four tables but the query I want to write involves three of them

CREATE TABLE `components` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(64) NOT NULL,
  `description` text DEFAULT NULL,
  `price` float unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name_UNIQUE` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=12 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

CREATE TABLE `products` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(64) NOT NULL,
  `description` text DEFAULT NULL,
  `tax_code` varchar(8) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name_UNIQUE` (`name`),
  KEY `name_idx` (`tax_code`),
  CONSTRAINT `name` FOREIGN KEY (`tax_code`) REFERENCES `tax_codes` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

CREATE TABLE `product_components` (
  `product_id` int(10) unsigned NOT NULL,
  `component_id` int(10) unsigned NOT NULL,
  `count` int(10) unsigned NOT NULL,
  PRIMARY KEY (`product_id`,`component_id`),
  KEY `fk_component_id_idx` (`component_id`),
  CONSTRAINT `fk_component_id` FOREIGN KEY (`component_id`) REFERENCES `components` (`id`),
  CONSTRAINT `fk_product_id` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

Now what I want to do is list all the products and for each product calculate the cost of all the components that product needs. So if a product needs 4 doodads that cost $1 and 7 whatzits that cost $2 the cost of the product would be $18 (41 + 72). I know I’d need some JOINs but I have no idea what I’d need.

    • CountVon@sh.itjust.works
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      1 year ago

      Side note, does the page say there’s 17 comments on this post for you?

      No, for me it says there are 7 comments but that’s still incorrect. When I manually count them I see 5 comments, not including the one I’m writing. I suspect edits might be getting counted as “new posts” by some instances. I gooned up the SQL pretty bad on the first attempt and edited it several times. There maybe something funky going on under the hood with federation as well that would explain why we’re getting different incorrect counts.