### Database Schema
CREATE TABLE `Products` (
`product_id` INTEGER PRIMARY KEY,
`product_name` VARCHAR(20),
`product_price` DECIMAL(19,4),
`product_description` VARCHAR(255)
)

CREATE TABLE `Addresses` (
`address_id` INTEGER PRIMARY KEY,
`address_details` VARCHAR(80),
`city` VARCHAR(50),
`zip_postcode` VARCHAR(20),
`state_province_county` VARCHAR(50),
`country` VARCHAR(50)
)

CREATE TABLE `Customers` (
`customer_id` INTEGER PRIMARY KEY,
`payment_method` VARCHAR(10) NOT NULL,
`customer_name` VARCHAR(80),
`customer_phone` VARCHAR(80),
`customer_email` VARCHAR(80),
`date_became_customer` DATETIME
)

CREATE TABLE `Regular_Orders` (
`regular_order_id` INTEGER PRIMARY KEY,
`distributer_id` INTEGER NOT NULL,
FOREIGN KEY (`distributer_id` ) REFERENCES `Customers`(`customer_id` )
)

CREATE TABLE `Regular_Order_Products` (
`regular_order_id` INTEGER NOT NULL,
`product_id` INTEGER NOT NULL,
FOREIGN KEY (`product_id` ) REFERENCES `Products`(`product_id` ),
FOREIGN KEY (`regular_order_id` ) REFERENCES `Regular_Orders`(`regular_order_id` )
)

CREATE TABLE `Actual_Orders` (
`actual_order_id` INTEGER PRIMARY KEY,
`order_status_code` VARCHAR(10) NOT NULL,
`regular_order_id` INTEGER NOT NULL,
`actual_order_date` DATETIME,
FOREIGN KEY (`regular_order_id` ) REFERENCES `Regular_Orders`(`regular_order_id` )
)

CREATE TABLE `Actual_Order_Products` (
`actual_order_id` INTEGER NOT NULL,
`product_id` INTEGER NOT NULL,
FOREIGN KEY (`product_id` ) REFERENCES `Products`(`product_id` ),
FOREIGN KEY (`actual_order_id` ) REFERENCES `Actual_Orders`(`actual_order_id` )
)

CREATE TABLE `Customer_Addresses` (
`customer_id` INTEGER NOT NULL,
`address_id` INTEGER NOT NULL,
`date_from` DATETIME NOT NULL,
`address_type` VARCHAR(10) NOT NULL,
`date_to` DATETIME,
FOREIGN KEY (`customer_id` ) REFERENCES `Customers`(`customer_id` ),
FOREIGN KEY (`address_id` ) REFERENCES `Addresses`(`address_id` )
)

CREATE TABLE `Delivery_Routes` (
`route_id` INTEGER PRIMARY KEY,
`route_name` VARCHAR(50),
`other_route_details` VARCHAR(255)
)

CREATE TABLE `Delivery_Route_Locations` (
`location_code` VARCHAR(10) PRIMARY KEY,
`route_id` INTEGER NOT NULL,
`location_address_id` INTEGER NOT NULL,
`location_name` VARCHAR(50),
FOREIGN KEY (`location_address_id` ) REFERENCES `Addresses`(`address_id` ),
FOREIGN KEY (`route_id` ) REFERENCES `Delivery_Routes`(`route_id` )
)

CREATE TABLE `Trucks` (
`truck_id` INTEGER PRIMARY KEY,
`truck_licence_number` VARCHAR(20),
`truck_details` VARCHAR(255)
)

CREATE TABLE `Employees` (
`employee_id` INTEGER PRIMARY KEY,
`employee_address_id` INTEGER NOT NULL,
`employee_name` VARCHAR(80),
`employee_phone` VARCHAR(80),
FOREIGN KEY (`employee_address_id` ) REFERENCES `Addresses`(`address_id` )
)

CREATE TABLE `Order_Deliveries` (
`location_code` VARCHAR(10) NOT NULL,
`actual_order_id` INTEGER NOT NULL,
`delivery_status_code` VARCHAR(10) NOT NULL,
`driver_employee_id` INTEGER NOT NULL,
`truck_id` INTEGER NOT NULL,
`delivery_date` DATETIME,
FOREIGN KEY (`truck_id` ) REFERENCES `Trucks`(`truck_id` ),
FOREIGN KEY (`actual_order_id` ) REFERENCES `Actual_Orders`(`actual_order_id` ),
FOREIGN KEY (`location_code` ) REFERENCES `Delivery_Route_Locations`(`location_code` ),
FOREIGN KEY (`driver_employee_id` ) REFERENCES `Employees`(`employee_id` )
)

### Question
Find the payment method that is used most frequently.

### SQL
SELECT payment_method FROM Customers GROUP BY payment_method ORDER BY count(*) DESC LIMIT 1