我仍然是mySQL的初学者。我一直在努力寻找项目触发因素，但无法提出解决方案。这是我想要做的：
下订单后，我想要一个触发器来更新库存。这里的障碍是订单可以有许多产品，而这些产品由库存的不同元素组成。这是我尝试过的方法，也许可以帮助您理解这个主意。
-- -----------------------------------------------------
-- Table `McDo`.`Order_details`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `McDo`.`Order_details` (
`orders_Order_id` INT NOT NULL,
`Products_Prod_ID` INT NOT NULL,
`Order_details_qty` INT NULL,
PRIMARY KEY (`orders_Order_id`, `Products_Prod_ID`),
INDEX `fk_orders_has_Products_Products1_idx` (`Products_Prod_ID`
ASC) VISIBLE,
INDEX `fk_Order_details_orders1_idx` (`orders_Order_id` ASC)
VISIBLE,
CONSTRAINT `fk_orders_has_Products_Products1`
FOREIGN KEY (`Products_Prod_ID`)
REFERENCES `McDo`.`Products` (`Prod_ID`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_Order_details_orders1`
FOREIGN KEY (`orders_Order_id`)
REFERENCES `McDo`.`Orders` (`Order_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `McDo`.`Inventory`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `McDo`.`Inventory` (
`Inv_ID` INT NOT NULL,
`Inv_type` VARCHAR(1) NOT NULL,
`Inv_name` VARCHAR(45) NULL,
`Inv_qty` INT NULL,
`Inv_price_unit` DECIMAL(20,2) NULL,
PRIMARY KEY (`Inv_ID`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `McDo`.`Recipes`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `McDo`.`Recipes` (
`Products_Prod_ID` INT NOT NULL,
`Inventory_Inv_ID` INT NOT NULL,
`Requiered_qty` INT NULL,
PRIMARY KEY (`Products_Prod_ID`, `Inventory_Inv_ID`),
INDEX `fk_Products_has_Inventory_Products1_idx` (`Products_Prod_ID` ASC)
VISIBLE,
INDEX `fk_Products_has_Inventory_Inventory1_idx` (`Inventory_Inv_ID`
ASC) VISIBLE,
CONSTRAINT `fk_Products_has_Inventory_Products1`
FOREIGN KEY (`Products_Prod_ID`)
REFERENCES `McDo`.`Products` (`Prod_ID`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_Products_has_Inventory_Inventory1`
FOREIGN KEY (`Inventory_Inv_ID`)
REFERENCES `McDo`.`Inventory` (`Inv_ID`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
and here a sample of the data
-- -----------------------------------------------------
-- Data for table `McDo`.`Recipes`
-- -----------------------------------------------------
START TRANSACTION;
USE `McDo`;
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 102, 3);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 103, 2);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 112, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 110, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 111, 2);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 114, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 113, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 108, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 101, 2);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 111, 2);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 103, 2);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 107, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 113, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 114, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 108, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 109, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (301, 204, 1);
INSERT INTO `McDo`.`Recipes` (`Products_Prod_ID`, `Inventory_Inv_ID`, `Requiered_qty`) VALUES (302, 202, 1);
-- -----------------------------------------------------
-- Data for table `McDo`.`Inventory`
-- -----------------------------------------------------
START TRANSACTION;
USE `McDo`;
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (101, 'C', 'regular bun', 1000, 0.07);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (102, 'C', 'sesame bun', 1000, 0.12);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (103, 'C', 'beef patty', 1000, 0.35);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (107, 'C', 'ketchup sachet', 5000, 0.02);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (108, 'C', 'seasoning sachet', 5000, 0.01);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (109, 'C', 'mustard sachet', 5000, 0.01);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (110, 'C', 'big mac sauce sachet', 5000, 0.04);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (111, 'C', 'cheese slice', 2000, 0.05);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (112, 'C', 'precut letuce', 1500, 0.02);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (113, 'C', 'precut onion', 1500, 0.01);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (114, 'C', 'precut pickle', 1500, 0.01);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (202, 'N', 'mc double wrapping', 1000, 0.01);
INSERT INTO `McDo`.`Inventory` (`Inv_ID`, `Inv_type`, `Inv_name`, `Inv_qty`, `Inv_price_unit`) VALUES (204, 'N', 'big mac box', 1000, 0.02);
这是3张桌子
1000,301,2;
1000,302,1;
1001,301,2;
1002,302,3;
订单如下：
input: a a a b b c !
Expected output:
Counts:
a 3
b 2
c 1
答案 0 :(得分：0)
允许您在更新查询中使用联接，所以也许
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