Multiply values ​of two variables according to id - sql

Question

I have a problem with the multiplication of two variables.
I have two sql statements with which I get the number of hours that an employee has worked during a specific month, and another statement to get the hourly cost that each employee has.
I must say that they are two different tables in the database.
What I would like is to multiply the hours of each employee by the hourly cost that employee has, and then add the results.
These two sentences work fine, if I do "print_r" I see the results that each employee has.
I guess I have to do it through the ID, but I don't know how to do it.
This is what I have so far, and I only get it to multiply the first person it finds.
$SumaHoras = $DB->Sql ("SELECT Id_Persona, CONCAT(SUM(Horas)* 3600)/36000000 as Hora FROM table1");
$SumaCosteHora = $DB->Sql("SELECT Id_CostPers, CONCAT(Coste_Hora) as Coste FROM table2");
$suma1 = [];
while($totalSumaHoras = $DB->Row($SumaHoras)){
$suma1 = $totalSumaHoras;
print_r($suma1);
}
$suma2 = [];
while($totalSumaCoste = $DB->Row($SumaCosteHora)){
$suma2 = $totalSumaCoste;
print_r($suma2);
}
$total4 = $suma1->Hora * $suma2->Coste;
I don't know if I explained myself well, but I appreciate any help you can offer me.

Answer 1

Your first line of code does not work - it generates errors - "The concat function requires 2 to 254 arguments." and then if you remove the CONCAT you get "Column 'table1.Id_Persona' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause." - as pointed out by #isamu
You should not use CONCAT for numbers - that returns a string - always use the correct Type for data.
To get all the information you require at once you need to use a JOIN see This article
E.g.
SELECT Id_Persona, t2.Coste_Hora * (SUM(t1.Horas) * 3600.0)/36000000.0
FROM table1 t1
INNER JOIN table2 t2 ON t1.Id_Persona = t2.Id_CostPers
group by Id_Persona, t2.Coste_Hora
I'm not sure why you are using that particular calculation but note I have appended .0 to those integer values to ensure that decimal calculation takes place - to explain what I mean try running these two lines of SQL
SELECT 10 * 3600/36000000;
SELECT 10 * 3600.0/36000000.0;