Sum specific keys in SQL query - PHP - php

Question

I have a SQL query that returns all fields in a table:
$registro = mysqli_query($con,
"SELECT * FROM agenda ORDER BY procedimento LIMIT $limit, $nroLotes");
My question is, if possible, through this query, sum the particular column values associated with another column of values, eg
Among other columns there are "Column: Name" where the values are names and "Column: Value" where the values are numbers. The idea is to add up the values associated with the names.
I suppose I do a foreach inside the while, but I have difficulty in this approach.
The following piece code in question:
<?php
//...
$registro = mysqli_query($con, "SELECT * FROM agenda ORDER BY procedimento LIMIT $limit, $nroLotes");
$tabela = $tabela.'<table class="table table-striped table-condensed table- hover">
<tr>
<th width="300">Nome</th>
<th width="200">Procedimentos</th>
<th width="150">Valor Cobrado do serviço</th>
<th width="150">Valor Total dos serviços</th>
<th width="150">Porcentagem do Valor Total dos serviços</th>
<th width="150">Data</th>
</tr>';
while($linha = mysqli_fetch_array($registro)){
$porcentagem = ($linha['valor'] * 30) / 100;
$tabela = $tabela.'<tr>
<td>'.$linha['nome_funcionario'].'</td>
<td>'.$linha['procedimento'].'</td>
<td>'.number_format($linha['valor'], 2, ',', '.').'</td>
<td>'.number_format($porcentagem).'</td>
<!--cell containing the sum-->
<!--<td>'.number_format($sum).'</td>-->
<td>'.fechaNormal($linha['start']).'</td>';
}
$tabela = $tabela.'</table>';
$array = array(0 => $tabela,
1 => $lista);
echo json_encode($array);
?>
I enjoy some light ;)