Select the employee who earned more - mysql

Question

[MySQL] I want to select the employee who earned more, the problem is that I am using two tables.
Finally I have no idea how to do it.
I built a query that can count the number of services and sort by most, but the query is flawed as there services with higher values​​.
here is the table structure.
CREATE TABLE IF NOT EXISTS `contas` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`id_servico` int(11) DEFAULT NULL,
`id_funcionario` int(11) DEFAULT NULL,
`data` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=28 ;
CREATE TABLE IF NOT EXISTS `servicos` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`titulo` varchar(250) NOT NULL COMMENT 'Título do serviço',
`descri` mediumtext COMMENT 'uma pequena descrição do serviço',
`valor` varchar(10) NOT NULL COMMENT 'valor bruto do serviço',
`comissao` varchar(10) DEFAULT NULL COMMENT 'comissão por funcionario',
`data` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=8 ;

Answer 1

Select all employees, join their "services", then group by employee ID, sum their income and select the first one.
SELECT E.id, SUM(S.amount) AS income
FROM employee E
INNER JOIN service S ON S.employee_id = E.id
GROUP BY E.id
ORDER BY income DESC
LIMIT 1