SELECT SUM(`order_details`.`UnitPrice` * `order_details`.`Quantity` - `order_details`.`Discount`) FROM `customers` 
LEFT JOIN `orders` ON `orders`.`CustomerID`=`customers`.`CustomerID` 
LEFT JOIN `order_details` ON `orders`.`OrderID`=`order_details`.`OrderID` 
WHERE `customers`.`CustomerID`='%ID%'

SELECT FLOOR(DATEDIFF(NOW(), `employees`.`BirthDate`) / 365) FROM `employees` 
WHERE `employees`.`EmployeeID`='%ID%'

DATEDIFF returns the difference between 2 dates in days, so we should divide by 365 to get years. Using FLOOR rounds down age to the nearest year ... That is, if someone is 32.4 years old, her age would display as 32. Also, if someone is 36.9 years old, she'd show as 36 years old since she's, technically, not 37 yet ;)

SELECT SUM(`order_details`.`UnitPrice` * `order_details`.`Quantity` - `order_details`.`Discount`) FROM `employees` 
LEFT JOIN `orders` ON `orders`.`EmployeeID`=`employees`.`EmployeeID` 
LEFT JOIN `order_details` ON `orders`.`OrderID`=`order_details`.`OrderID` 
WHERE `employees`.`EmployeeID`='%ID%'

SELECT
IF(
    `orders`.`ShippedDate`, 
        '<span class="text-success">Shipped</span>', 
        /* else */
        IF(
           `orders`.`RequiredDate` < now(), 
                '<span class="text-danger">Late</span>', 
                /* else */
                '<span class="text-warning">Pending</span>'
        )
) 
FROM `orders` 
WHERE `orders`.`OrderID`='%ID%'

For late orders, a Late status would be displayed. For orders not yet shipped, but not late, a Pending status would be displayed. And for shipped orders, Shipped will be displayed.

SELECT SUM(`order_details`.`UnitPrice` * `order_details`.`Quantity`) + `orders`.`Freight` FROM `orders` 
LEFT JOIN `order_details` ON `order_details`.`OrderID`=`orders`.`OrderID` 
WHERE `orders`.`OrderID`='%ID%'

SELECT `order_details`.`UnitPrice` * `order_details`.`Quantity` - `order_details`.`Discount` FROM `order_details` 
WHERE `order_details`.`odID`='%ID%'

The formula above calculates the subtotal of this invoice line by multiplying unit price by quantity and then subtracting discount amount.

SELECT COUNT(1) FROM `shippers` 
LEFT JOIN `orders` ON `orders`.`ShipVia`=`shippers`.`ShipperID` 
WHERE `shippers`.`ShipperID`='%ID%'