error of 1824: failed to open the referenced table - mysql

Question

Not sure what i'm doing wrong here. Im trying to understand the relationships between tables? Please help thank you
DROP DATABASE IF EXISTS `sql_retail`;
CREATE DATABASE `sql_retail`;
USE `sql_retail`;
SET NAMES utf8 ;
SET character_set_client = utf8mb4 ;
CREATE TABLE `RETAIL_ORDER` (
`OrderNumber` int(4) NOT NULL,
`StoreNumber` int(2) NOT NULL,
`StoreZip` char(9) NOT NULL,
`OrderMonth` char(12) NOT NULL,
`OrderYear` int(4) NOT NULL,
`OrderTotal` float(10) NOT NULL,
PRIMARY KEY (`OrderNumber`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
INSERT INTO `RETAIL_ORDER` VALUES (1000, 10, 98110, 'December', 2017, 445.00);
INSERT INTO `RETAIL_ORDER` VALUES (2000, 20, 02335, 'December', 2017, 310.00);
INSERT INTO `RETAIL_ORDER` VALUES (3000, 10, 98110, 'January', 2018, 480.00);
CREATE TABLE `ORDER_ITEM` (
`OrderNumber` int(11) NOT NULL,
`SKU` int(7) NOT NULL,
`Quantity` int(6) NOT NULL,
`Price` float(10) NOT NULL,
`Extended Price` float(10) NOT NULL,
PRIMARY KEY (`OrderNumber`),FOREIGN KEY(`OrderNumber`)REFERENCES RETAIL_ORDER(`OrderNumber`),
FOREIGN KEY(`SKU`)REFERENCES SKU_DATA(`SKU`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
INSERT INTO `ORDER_ITEM` VALUES (1000, 201000, 1, 300.00, 300.00);
INSERT INTO `ORDER_ITEM` VALUES (1000, 202000, 1, 130.00, 130.00);
INSERT INTO `ORDER_ITEM` VALUES (2000, 101100, 4, 50.00, 200.00);
INSERT INTO `ORDER_ITEM` VALUES (2000, 101200, 2, 50.00, 100.00);
INSERT INTO `ORDER_ITEM` VALUES (3000, 100200, 1, 300.00, 300.00);
INSERT INTO `ORDER_ITEM` VALUES (3000, 101100, 2, 50.00, 100.00);
INSERT INTO `ORDER_ITEM` VALUES (3000, 101200, 1, 50.00, 50.00);
CREATE TABLE `SKU_DATA` (
`SKU` int(11) NOT NULL,
`SKU_Description` varchar(50) NOT NULL,
`Department` varchar(20) NOT NULL,
`Buyer` varchar(15) NOT NULL,
PRIMARY KEY (`SKU`),FOREIGN KEY(`Buyer`)REFERENCES BUYER(`BuyerName`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
INSERT INTO `SKU_DATA` VALUES (100100, 'Std. Scuba Tank, Yellow', 'Water Sports', 'Peter Hansen');
INSERT INTO `SKU_DATA` VALUES (100200, 'Std. Scuba Tank, Magenta', 'Water Sports', 'Peter Hansen');
INSERT INTO `SKU_DATA` VALUES (100300, 'Std. Scuba Tank, Light Blue', 'Water Sports', 'Peter Hansen');
INSERT INTO `SKU_DATA` VALUES (100400, 'Std. Scuba Tank, Dark Blue', 'Water Sports', 'Peter Hansen');
INSERT INTO `SKU_DATA` VALUES (100500, 'Std. Scuba Tank, Light Green', 'Water Sports', 'Peter Hansen');
INSERT INTO `SKU_DATA` VALUES (100600, 'Std. Scuba Tank, Dark Green', 'Water Sports', 'Peter Hansen');
INSERT INTO `SKU_DATA` VALUES (101100, 'Dive Mask, Small Clear', 'Water Sports', 'Nancy Meyers');
INSERT INTO `SKU_DATA` VALUES (101200, 'Dive Mask, Med Clear', 'Water Sports', 'Nancy Meyers');
INSERT INTO `SKU_DATA` VALUES (201000, 'Half dome tent', 'camping', 'Cindy Lo');
INSERT INTO `SKU_DATA` VALUES (202000, 'Half dome tent vestibule', 'camping', 'Cindy Lo');
INSERT INTO `SKU_DATA` VALUES (203000, 'Half dome tent vestibule wide', 'camping', 'Cindy Lo');
INSERT INTO `SKU_DATA` VALUES (301000, 'Light fly climbing harness', 'climbing', 'Jerry Martin');
INSERT INTO `SKU_DATA` VALUES (302000, 'Locking Carabiner, Oval', 'climbing', 'Jerry Martin');
CREATE TABLE `BUYER` (
`BuyerName` varchar(15) NOT NULL,
`Department` varchar(15) NOT NULL,
`Position` varchar(15) NOT NULL,
`Supervisor` varchar(15) NOT NULL,
PRIMARY KEY (`BuyerName`),FOREIGN KEY(`Supervisor`)REFERENCES BUYER(`BuyerName`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
INSERT INTO `SKU_DATA` VALUES ('Cindy Lo', 'Purchasing', 'Buyer 2', 'Mary Smith');
INSERT INTO `SKU_DATA` VALUES ('Jerry Martin', 'Purchasing', 'Buyer 1', 'Cindo Lo');
INSERT INTO `SKU_DATA` VALUES ('Mary Smith', 'Purchasing', 'Manager','' );
INSERT INTO `SKU_DATA` VALUES ('Nancy Meyers', 'Purchasing', 'Buyer 1', 'Pete Hansen');
INSERT INTO `SKU_DATA` VALUES ('Pete Hansen', 'Purchasing', 'Buyer 3', 'Mary Smith');

Answer 1

You have some errors.
First you assign a foreign key to a table that don't exists yet and second you have duplicate values into your inserts for your primary keys.
I have fixed your table creation, check your insert datas.
Follow below approach to create your tables and then do the inserts:
DROP DATABASE IF EXISTS sql_retail ;
CREATE DATABASE sql_retail ;
USE sql_retail ;
SET NAMES utf8 ;
SET character_set_client = utf8mb4 ;
CREATE TABLE `RETAIL_ORDER` (
`OrderNumber` int(4) NOT NULL,
`StoreNumber` int(2) NOT NULL,
`StoreZip` char(9) NOT NULL,
`OrderMonth` char(12) NOT NULL,
`OrderYear` int(4) NOT NULL,
`OrderTotal` float(10) NOT NULL,
PRIMARY KEY (`OrderNumber`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
CREATE TABLE `ORDER_ITEM` (
`OrderNumber` int(11) NOT NULL,
`SKU` int(7) NOT NULL,
`Quantity` int(6) NOT NULL,
`Price` float(10) NOT NULL,
`Extended Price` float(10) NOT NULL,
PRIMARY KEY (`OrderNumber`),
FOREIGN KEY(`OrderNumber`)REFERENCES RETAIL_ORDER(`OrderNumber`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
CREATE TABLE `SKU_DATA` (
`SKU` int(11) NOT NULL,
`SKU_Description` varchar(50) NOT NULL,
`Department` varchar(20) NOT NULL,
`Buyer` varchar(15) NOT NULL,
PRIMARY KEY (`SKU`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
ALTER TABLE ORDER_ITEM ADD FOREIGN KEY(`SKU`)REFERENCES SKU_DATA(`SKU`);
CREATE TABLE `BUYER` (
`BuyerName` varchar(15) NOT NULL,
`Department` varchar(15) NOT NULL,
`Position` varchar(15) NOT NULL,
`Supervisor` varchar(15) NOT NULL,
PRIMARY KEY (`BuyerName`),
FOREIGN KEY(`Supervisor`)REFERENCES BUYER(`BuyerName`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
ALTER TABLE SKU_DATA ADD FOREIGN KEY(`Buyer`)REFERENCES BUYER(`BuyerName`);
Demo: https://www.db-fiddle.com/f/7yUJcuMJPncBBnrExKbzYz/28