Lab2-TransactionsTriggersAndCheckConstraints.sql

-- STEP 1
CREATE TABLE `employees_undo` (
 `date_of_change` timestamp(2) NOT NULL DEFAULT CURRENT_TIMESTAMP(2)
COMMENT 'Records the date and time when the data was manipulated. This will 
help to keep track of the changes made. The assumption is that no 2 users 
will change the exact same record at the same time (with a precision of a 
hundredth of a second, e.g., 4.26 seconds).',
 `employeeNumber` int NOT NULL,
 `lastName` varchar(50) DEFAULT NULL,
 `firstName` varchar(50) DEFAULT NULL,
 `extension` varchar(10) DEFAULT NULL,
 `email` varchar(100) DEFAULT NULL,
 `officeCode` varchar(10) DEFAULT NULL,
 `reportsTo` int DEFAULT NULL,
 `jobTitle` varchar(50) DEFAULT NULL,
 `change_type` varchar(50) NOT NULL COMMENT 'Records the type of data 
manipulation that was done, for example an insertion, an update, or a 
deletion.',
 PRIMARY KEY (`date_of_change`),
 UNIQUE KEY `date_of_change_UNIQUE` (`date_of_change`)
) ENGINE=InnoDB;

-- STEP 2
CREATE
 
 TRIGGER TRG_BEFORE_UPDATE_ON_employees
 BEFORE UPDATE ON employees FOR EACH ROW
 
 INSERT INTO `employees_undo` SET
 `date_of_change` = CURRENT_TIMESTAMP(2),
 `employeeNumber` = OLD.`employeeNumber` ,
 `lastName` = OLD.`lastName` ,
 `firstName` = OLD.`firstName` ,
 `extension` = OLD.`extension` ,
 `email` = OLD.`email` ,
 `officeCode` = OLD.`officeCode` ,
 `reportsTo` = OLD.`reportsTo` ,
 `jobTitle` = OLD.`jobTitle` ,
 `change_type` = 'An update DML operation was executed';


-- STEP 4
UPDATE `employees` 
SET
`lastName` = 'Muiruri'
WHERE
`employeeNumber` = '1056';

UPDATE `employees` 
SET
`email` = 'mmuiruri@classicmodelcars.com'
WHERE
`employeeNumber` = '1056';


-- STEP 5
CREATE TABLE `customers_data_reminders` (
    `customerNumber` INT NOT NULL COMMENT 'Identifies the customer whose data 
    is partly missing',
    `customers_data_reminders_timestamp` TIMESTAMP(2) NOT NULL DEFAULT CURRENT_TIMESTAMP (2) COMMENT 'Records the time when the missing data was 
    detected',
    `customers_data_reminders_message` VARCHAR(100) NOT NULL COMMENT 'Records 
    a message that helps the customer service personnel to know what data is 
    missing from the customer\'s record',
    `customers_data_reminders_status` TINYINT NOT NULL DEFAULT '0' COMMENT 'Used to record the status of a reminder (0 if it has not yet been 
    addressed and 1 if it has been addressed)',
    PRIMARY KEY (`customerNumber` , `customers_data_reminders_timestamp` , `customers_data_reminders_message` , `customers_data_reminders_status`),
    CONSTRAINT `FK_1_customers_TO_M_customers_data_reminders` FOREIGN KEY (`customerNumber`)
        REFERENCES `customers` (`customerNumber`)
        ON DELETE CASCADE ON UPDATE CASCADE
)  ENGINE=INNODB COMMENT='Used to remind the customer service personnel 
about a client\'s missing data. This enables them to ask the client to 
provide the data during the next interaction with the client.';

-- STEP 6
DELIMITER $$
CREATE TRIGGER TRG_AFTER_INSERT_ON_customers
AFTER INSERT ON customers FOR EACH ROW
BEGIN
 IF NEW.postalCode IS NULL THEN
 INSERT INTO `customers_data_reminders`
 (`customerNumber`, `customers_data_reminders_timestamp`,
`customers_data_reminders_message`)
 VALUES (NEW.customerNumber, CURRENT_TIMESTAMP(2), 'Please remember to record the client\'s postal code');
 END IF;
 IF NEW.salesRepEmployeeNumber IS NULL THEN
 INSERT INTO `customers_data_reminders`
 (`customerNumber`, `customers_data_reminders_timestamp`,
`customers_data_reminders_message`)
 VALUES (NEW.customerNumber, CURRENT_TIMESTAMP(2), 'Please remember to assign a sales representative to the client');
 END IF;
 IF NEW.creditLimit IS NULL THEN
 INSERT INTO `customers_data_reminders`
 (`customerNumber`, `customers_data_reminders_timestamp`,
`customers_data_reminders_message`)
 VALUES (NEW.customerNumber, CURRENT_TIMESTAMP(2), 'Please remember to set the client\'s credit limit');
 END IF;
END$$
DELIMITER ;

-- STEP 7
INSERT INTO `customers` 
(`customerNumber`, `customerName`, `contactLastName`, `contactFirstName`, `phone`, `addressLine1`, `city`, `country`)
VALUES
('497', 'House of Leather', 'Wambua', 'Gabriel', '+254 720 123 456', '9 Agha Khan Walk', 'Nairobi', 'Kenya');

--
SELECT
 *
FROM
 customers_data_reminders;
 
 --
DELETE FROM `customers` WHERE `customerNumber` = '497';

--

INSERT INTO `customers` 
(`customerNumber`, `customerName`, `contactLastName`, `contactFirstName`, `phone`, `addressLine1`, `city`, `country`, `salesRepEmployeeNumber`)
VALUES
('497', 'House of Leather', 'Wambua', 'Gabriel', '+254 720 123 456', '9 Agha Khan Walk', 'Nairobi', 'Kenya', 1401);

--

SELECT
 *
FROM
 customers_data_reminders;

--

UPDATE `customers` SET `postalCode` = '00100' WHERE `customerNumber` =
'497';

--

SELECT
 *
FROM
 customers_data_reminders;

-- STEP 8

CREATE TABLE part (
 part_no VARCHAR(18) PRIMARY KEY,
 part_description VARCHAR(255),
 part_supplier_tax_PIN VARCHAR (11) CHECK (part_supplier_tax_PIN REGEXP'^[A-Z]{1}[0-9]{9}[A-Z]{1}$'),
 part_supplier_email VARCHAR (55),
 part_buyingprice DECIMAL(10,2 ) NOT NULL CHECK (part_buyingprice >= 0),
 part_sellingprice DECIMAL(10,2) NOT NULL,
 CONSTRAINT CHK_part_sellingprice_GT_buyingprice CHECK (part_sellingprice >= part_buyingprice),
 CONSTRAINT CHK_part_valid_supplier_email CHECK (part_supplier_email 
REGEXP '^[a-zA-Z0-9]{3,}@[a-zA-Z0-9]{1,}\\.[a-zA-Z0-9.]{1,}$')
);

-- STEP 9
DELIMITER //
CREATE TRIGGER TRG_BEFORE_UPDATE_ON_part 
BEFORE UPDATE ON part FOR EACH ROW
BEGIN
 DECLARE errorMessage VARCHAR(255);
 DECLARE EXIT HANDLER FOR SQLSTATE '45000'
 BEGIN
 RESIGNAL SET MESSAGE_TEXT = errorMessage;
 END;
 SET errorMessage = CONCAT('The new selling price of ',
NEW.part_sellingprice, ' cannot be 2 times greater than the current selling 
price of ', OLD.part_sellingprice);
 IF NEW.part_sellingprice > OLD.part_sellingprice * 2 THEN
 SIGNAL SQLSTATE '45000';
 END IF;
END//
DELIMITER ;